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LippiNCOTT's College Texts 

AGRICULTURE 

EDITED BY K. C. DAVIS, Ph.D. (Cornell) 

SOIL PHYSICS AND 
MANAGEMENT 






jfG?']\tosiER, B.S. 



PROFESSOR OF SOIL PHYSICS, UNIVERSITY OF ILLINOIS; CHIEF OF SOIL PHYSICS, 
AGRICULTURAL EXPERIMENT STATION 

AND 

a^^f/gustafson, M.S. 

ASSISTANT PROFESSOR OF SOIL PHYSICS, UNIVERSITY OF ILLINOIS; ASSISTANT 
CHIEF OF SOIL PHYSICS, AGRICULTURAL EXPERIMENT STATION 



W£ ILLUSTRATIONS IN THE TEXT 




PHILADELPHIA & LONDON 
J. B. LIPPINCOTT COMPANY 



,VA^5 



COPyRlQHT, I917, BT J. B. LIPPINCOTT COMPANT 



Electrotyped and Printed by J. B. Lippincott Company 
The Washington Square Press, Philadelphia, U. S. A. 

DEC 19 1917 
©CI.A4 79588 



PREFACE 

This book is written for three purposes: first, as a text-book 
for agricultural students ; second, as a reference book for the prac- 
tical farmer; and, third, as an aid to the land owner who desires 
information in the personal management of his land. 

Soil physics is the application of physics to soils. It is so 
closely related to other sciences that it becomes necessary to trespass 
upon the ground of some of them, notably botany, geology, chem- 
istry, and zoology, to present certain subjects clearly and com- 
pletely. Soil physics dovetails in with the closely-related phases 
of agronomy, as soil biology, soil fertility, crop production, and 
agricultural engineering, to such an extent that it is necessary to 
give material very closely related to all of these. 

An attempt has been made to emphasize the principles of soil 
physics, omitting the details of practice except where necessary for 
purposes of illustration. Although the book is vrritten in the Middle 
AYest, yet the principles given apply anywhere. 

The arrangement of the matter presented has been carefully 
planned from the teaching standpoint, and has been tested in the 
classroom for several years. 

"Various sources of information have been used by the authors 
and acknowledgment made accordingly. 



J. G. MOSIER, 

A. F. GusTAFSO]sr. 



College of Agriculture, 

University of Illinois, 

Urbana, 111"., October, 1917. 



CONTENTS 



CHAPTER PAGE 

I. Soil Material and Its Origin 1 

Definition of Soil — Elements of the Earth's Crust — Soil 
Forming Minerals — Rocks — Igneous Rocks — Aqueous 
Rocks — ^Metamorpliic Rocks. 

II. Weathering 11 

Physical Agencies — Heat and Cold — Freezing and Thaw- 
ing — Glaciers — Erosion of Streams — Waves — Wind — ■ 
Plants — Chemical Agencies — Acids — Carbon Dioxide — 
Oxidation — Deoxidation — Hydration — ^ Solution — Plants 
— Animals. 

III. The Placing of Soil Material. I. Residual, Gravity- 

laid AND Water-laid Deposits 27 

Sedentary Formations — -Residual Soils — Cumulose Soils — 
Swamps and Marshes — ^Transported Formations — Col- 
luvial or Gravity-laid Soils — Sedimental or Water-laid 
Soils. 

IV. The Placing of Soil Material. II. Glacial or Ice-laid 

Deposits 41 

The Glacial Period — The Jerseyan or Nebraskan Glacia- 
tion — The Kansan Glaciation — The lllinoisan Glaciation 
— The lowan Glaciation — The Early Wisconsin Glaciation 
— -The Late Wisconsin Glaciation — Incidental Features. 

V. The Placing of Soil Material. III. Eolial or Wind- 
laid Deposits 53 

Classes of Wind-laid Material — Dunes — Loess — Adobe — 
Volcanic Dust. 

VI. Soil and Subsoil 67 

The Top Soil — ^Surface — Subsurface — Subsoil — Tight Clay 
— Hard Pan — Humid and Arid Subsoils — Plow Sole. 

VII. Classification of Soils 72 

Need of Classification — Basis of Classification — Geological 
— Lithological, — Temperature- — Moisture — Aiid Soils — 
Humid Soils — ^^''egetation — Color — Texture . 

VIII. Classification by the Bureau of Soils 78 

Soil Province — ^Soil Region — Soil Class — Soil Type — Pied- 
mont Plateau Province — Appalachian INIountain and Pla- 
teau Pro^ance — Limestone Valleys and Uplands Province — ■ 
Glacial and Loessial Province — Glacial Lake and River 
Terrace Province — Atlantic and Gulf Coastal Plains 
Province — River Flood Plains Province — Great Plains 
Region — Rocky Mountain and Plateau Region — North- 
western Intermountain Region — Great Basin Region — • 
Arid Southwest Region — Pacific Coast Region. 

V 



CONTENTS 

IX. Sub-provinces, Classes, Types, and Surveys 112 

Sub-provinces — Soil Classes — Soil Types — Naming of Soil 
Types — -Classes, Tj-pes, and Phases in Illinois — -Soil 
Surveys — Surveys in Different States — Objects of a Soil 
Survey — Methods of the Survey — Sampling of Soils. 

X. MiNER-AL Constituents 123 

Soil Particles and Theii" Separation — Mechanical or Phj-si- 
cal Analysis — ^Methods of — -Mineral Soil Constituents and 
Their Properties — Colloids — Colloids in Soils — ^Mineral 
Colloids — Claj's and Clay Loams — Silt and Silt Loams — 
Sands and Sand}' Loams — Gravel and Gravelly Loams — 
Stones. 

XL Organic Constituents of Soils 142 

Kinds of Organic Matter — Amount of Organic INIatter m 
Soils — Changes of Organic Matter — Nitrogen Content of 
Humus — Distribution of Organic ^Matter in the Soil Strata 
— Value of Organic Matter to Soils — Losses of Organic 
Matter — ^Estimation of Organic Matter. 

XII. IMaintaining and Increasing the Organic-matter 

Content of Soils 158 

Addition of Limestone — -Application of Phosphorus — 
Accumulations in Pastures — Green ^Manures — Catch and 
Cover Crops — Barnyard Manures — ^Loss of Manure and 
Its Prevention — Methods of Applying ^Manure — Organic 
Residues — -Growing Non-tilled Crops — Rotatio uof Crops. 

XIII. Physical Properties of Soils 175 

Real or Absolute Specific Gravity — Apparent Specific 
Gra^dty — Weight of the Soil — -Color of Soils — -Odor of Soils 
— Number of Particles — ^3hape of Particles — Arrangement 
of Particles — Internal Area of Surface — Porositj^ of Soils. 

XIV. Water op Soils . . 186 

Some Physical Characteristics of Water — Specific Heat — ■ 
Viscosity- — Uses of Water — ,\mount of '\^'ater Required 
by Plants — Dependent Upon Transpiration— Supply of 
Moisture in Soils — Ways of Expressing ]\Ioisture Content. 

XV. W.\ter of Soils. I. Hygroscopic Moisture 194 

Determination of Hygroscopic Coefficient of Soils — Use of 
Hygroscopic ^loisture. 

XVI. Water of Soils. II. Capillary W.^ter 199 

Surface Tension — ^Moisture in Soil Columns — Effect of 
Size of Soil Particles — Aloisture Equivalent — Determina- 
tion of i^Ioisture Equivalents from Other Soil Constants — 
[Movement — Tliickness of the Film — Mscosity — Te.xture — - 
Organic flatter — Maximum Capillary Capacity or Moist- 
ure-holding Capacity of Soils — Amount of Water Moved 
by Capillarity — -The Capillary Pull of Soils — Osmosis in 
Soils — -Use of Capillary Water — -Wilting Coefficient — 
Available ^loisture. 

XVII. W.^TER OF Soils. III. Gr-^a-itational Water 217 

Percolation — Physical Composition or Texture — -Granula- 
tion — Organic Matter — Viscosity — Atmospheric Pressure 
— Shrinkage Cracks — Roots of Plants — L3'simeters or 
Drain Gages. 



CONTENTS vii 

XVIII. Control of Moisture. I. Drainage 222 

Removal of Excess of Water — Stability — -Granulation — ■ 
Available Moisture — Aeration — Temperature^ — Decompo- 
sition and Nitrification — Heaving — -Erosion — -Types of 
Drainage — Open Drains — -Tile Drains. 

XIX. Control of Moisture. II. Tillage 230 

Moisture Capacity of Soils — Excess of Moisture — Losses 
from Soils — Artificial and Soil Mulches — -Fineness of 
Mulch — Depth of Mulch^Maintenance of Mulch. 

XX. Control of Moisture. III. Dry-land Agriculture 238 

Adaptation of a Region to Dry Farming — Water Require- 
ments of Plants — Loss of Water — Method of Preventing 
Loss of Water — Tillage — System of Cropping— Crops for 
Dry Farming — -Seeding — Acclimated Seed. 

XXI. Control of Moisture. IV. Irrigation 257 

Area and Projects — Sources of Water — ^Preparation of 
Land for Irrigation — ^Character of Water Used for Irriga- 
tion — Composition of River Sediments — Time of Irrigation 
— Amount of Water to Apply — Loss of Water from Canals 
— Duty of Water — Duty of Water in Different Countries — 
Measurement and Distribution of Water — Methods of 
Irrigation — Cultivation after Irrigation — Crops for Irri- 
gated Lands — Irrigation in Humid Climates. 

XXII. Alkali Lands and Their Reclamation 278 

Origin of Alkah — -Kinds of Alkah — Effect on Physical 
Condition of Soil — ^Vertical and Horizontal Distribution — ■ 
Effect of Irrigation on Rise of Alkah — -Effect of Alkali on 
Plants — Limit for Germination and Growth — UtiUzation 
and Reclamation of Alkali Lands — Growing Alkali- 
resistant Crops — Retarding Evaporation — Deep Plowing 
and Turning Under Alkah — ^Neutrahzing Black Alkah — 
Removing the Salts from the Soil — Hardpan — Value of 
Alkah Land — Alkah Soils of Humid Regions. 

XXIII. Temperature 293 

Sources of Soil Heat — Direct Radiation from the Sun 
— Precipitation — Chemical Changes — -Physical Changes — ■ 
Loss of Heat — ^Radiation — -Conduction into the Soil — • 
Evaporation of "SA^ater — Convection Currents of Air — Soil 
Temperature for Vital Functions of Plants — Tempera- 
ture for Germination — Temperature for Growth — Tem- 
peratures Favorable for Osmosis and Diffusion — ^Tempera- 
tures for Nitrification — Conditions Affecting Soil Tempera- 
ture — Specific Heat — -Evaporation of W^ater — Drainage — • 
Presence of Water — Absorption and Radiation of Heat — 
Latitude or Angle of Sun's Rays — Conductivity of Soil 
Material and Soils — -TiUage. 

XXIV. Soil Air and Aeration 309 

Use of Air in Soils — Amount of Air in Soils — -Composition 
of Soil Air — Aeration or Soil Ventilation — Water-logged 
Soil — ^Running Together. 



viii CONTENTS 

XXV. Soil Organisms 315 

Macro-organisms — -Rodents — Insects — Worms — Plants 

Micro-organisms — -Injurious Organisms — ^Beneficial Organ- 
isms — Distribution and Conditions for Their Activity — ■ 
Distribution — -Conditions for Development — Loss of Ni- 
trates — -Leaching — Denitrification. 

XXVI. Tillage 325 

Objects of Tillage — Pulverizing and Loosening the Soil 
— -Turning Under Vegetable Matter — -Killing Weeds — 
Storing and Conserving Moisture — Compacting the Soil 
— Planting the Seed — Implements of Tillage — Plows — 
Harrows — Compacters — -Seeders — ^Cultivators — ^Plowing — ■ 
Time of Plowing — ^Depth of Plowing — -Dynamiting — -Effect 
of Deep-rooting Crops — -Preparation of the Seed Bed — 
Wheat — Corn — -Oats — Cultivation — -Value of Mulch — 
Root Injury — -Level Cultivation. 

XXVII. Soil Erosion 358 

Cause of Erosion — ^Effect of Topography — -Texture and 
Structure of the Soil — Vegetative Covering — Character of 
the Rainfall — Results of Erosion — Removal of Organic 
Matter and Nitrogen — ^Changes Physical Character of 
Soil — Changes of Color— Ivinds of Erosion — Sheet Erosion 
— Methods of Prevention and Reclamation — Application 
of Limestone — ^Protection by Crops — -Residues — Increas- 
ing the Organic Matter — Deep Contour Plowing — Contour 
Seeding — Terraces — - Reforesting — Tiling — Gullying — - 
Methods of Prevention and Filhng — -Straw-brush — Dams 
— -Vegetation — Filhng with Soil. 

XXVIII. Rotation 376 

Advantages of Rotation — -Better Distribution of Work — • 
Control of Insects and Plant Diseases — Control of Weeds — 
Variation in Depth of Root Systems — -Maintenance of 
Good Tilth — Maintenance of Organic Matter — Toxic 
Substances — -Increased Yields — Planning a Rotation — • 
Places in Rotations for Crops — ^Practical Rotations — ^Corn 
and Winter Wheat Belt — Cotton Belt — Hay and Pasture 
Province — Spring Wheat Region — Great Plains Province. 

Appendix I. Soil Fertility 389 

Permanent Agriculture — Are Soils Inexhaustible? — -Plant 
Food Elements — Removal of Plant Food — -Crop Require- 
ments — -Supply of Plant Food in Soils — -Nitrogen — 
Phosphorus — Potassium — Other Elements. 

Appendix II 407 

Average Yield of Crops Per Acre by States in United States, 
Ten-year Average, 1906-1915 — Average Yield of Wheat 
Per Acre for Ten Years, 1905-1914, United States and 
European Countries. 

Appendix III 410 

Farm Land Value Per Acre — Farm Property Value — Corn 
Acreage — Corn Production — -Oats Production — Spring 
Wheat Acreage — Winter Wheat Acreage — Wheat Produc- 
tion. 



ILLUSTRATIONS 



*^^- PAGE 

Map Showing the Soil Provinces and Soil Regions of the United 
States Frontispiece 

1. Limestone Composed Chiefly of Shells of Brachiopods 9 

2. Limestone Containing Large Amounts of Crinoid Stems 9 

3. Irregular Weathering of Rock Due to Joints and Stratification 11 

4. A More x4dvanced Stage of Weathering 12 

5. "Capitol Rock," Butte, Montana 12 

6. Exfoliated Granite in the Sierra Nevadas, California 13 

7. Columbia Glacier Overriding a Forest, Alaska 14 

8. Front of Columbia Glacier in 1910 Compared in Height to Bunker 

Hill Monument 15 

9. The Material Carried and Rolled by Streams Gives Them Their Great 

Eroding Power 16 

10. Inner Gorge of Grand Canon of the Colorado River, Arizona 17 

11. Wind-carved Granite 18 

12. The Roots of Trees Form Wedges for Prying Rocks Apart 19 

13. Stalactites and Stalagmites Formed in a Cavern from Limestone- 

Dissolved by Carbonated Water While Passuag Through the 

Rocks Above 23 

14. Sinkholes in a Cave Region — Southern Illinois , 24 

15. The Outlets of Sinkholes Sometimes Become Clogged and " Sinlvhole '.' 

Ponds Result 24 

16. Ox-bow Lakes Formed by Shifting of Channel 28 

17. Typical Eastern Swamp Land 29 

18. Florida Everglades 29 

19. Section Showing One Step in the Filling of the Lake with Peat 29 

20. Hummocks 6 to 12 Inches High Found in Swampy Places Produced 

by Trampling of Stock 30 

21. Weathering of Jointed Rock Above and Thin Bedded Beneath 31 

22. Rock Disintegration and Formation of Talus Slope 32 

23. The Side of a Ravine Near Crawfordsville, Indiana 32 

24. Mud Flow 34 

25. Map Showing the Early Stages in the Formation of Coast IMarshes. . 36 

26. Section of Marine Marsh 36 

27. Mangrove Marsh, Biscayne, Florida 37 

28. Level Floor of Lake Chicago, with the Shore-Une in the Distance ... 37 

29. Terraces of Frazier River at Lilloet, B. C 38 

30. Terrace Along Creek, Near Rockford, Illinois, Showing Stratification 38 

31. Closer View Section of Gravel Terrace of Fig. 30 39 

32. Front of Chenega Glacier Compared with Washington Monument, 

550 Feet High 41 

33. Very Stony and Gravelly Phase of Glacial Drift Near "VMiitewater, 

Wisconsin 41 

34. Limestone Boulder Showing Glacial Scratches, Urbana, 111 42 

35. Glacial Grooves or Strife on Rock Surface, Northern Ohio 43 

36. Typical Topography- of Terminal Moraine Near Ocomowoc, Wisconsin 43 

37. Drumlins — Remnants of Former Terminal Moraines 44 

38. Drumlins — Transverse View 44 

39. Adeline Esker, Ogle County, Illinois 44 

40. The Material Composing Adeline Esker Consists of Coarse Sand and 

Gravel 45 



X ILLUSTRA.TIONS 

41. Map Showing Extent and Southern Limit of Glaciation in North 

America 46 

42. Map Showing the Three Centers of Ice Accumulation in North 

America 47 

43. Map Showing Extent of Ice-sheet, Europe 48 

44. A Section Showing the Black Sangamon Soil with the Uhnois Glacial 

Drift Beneath and the lowan Loess Above, with the Present Soil 

on the Surface 49 

45. A Section Showing Bloomington Gravel, Shelb3rville TUl Sheet, lowan 

Loess, Sangamon Soil, Silt Below Peat 49 

46. Granite Boulder Weighing About 30 Tons, at Depot of Northwestern 

R. R., Waukegan, Illinois 51 

47. Heap of Boulders Collected from a Moraine in Northern Illinois .... 51 

48. A Dust Storm in Kansas, May 26, 1912 . . 54 

49. Sand Dune Advancing Over Forest, Beaufort Harbor, N. C 55 

50. A Resurrected Forest, Dune Park, Indiana 55 

51. Wind Ripples on Sand Dune 56 

52. Transplanting Beach or Marram Grass 56 

53. The Grass in the Foreground Holds the Sand Which Drifts from the 

"Waste" Beyond the Fence 57 

54. Sand is Being Held by Vegetation 57 

55. Fences Being Used to Check the Movement of Sand 58 

56. Large "Blowout" in Sand Ai-ea, Mason County, Illinois 59 

57. Black Locusts Growing on Sand to the Right, Drifting Sand on Left. 59 

58. The Traihng Wild Bean Makes a Large Growth 60 

59. Pines Growing on Sand Dunes in England 60 

60. Alluviation by Glacial Stream, Below Hidden Glacier, Alaska 62 

61. Calcium Carbonate Concretions from the Loess of Illinois 63 

62. A Road Through a Deposit of Deep Loess Along the Lower Illinois 

River 63 

63. Map of United States, Showing Timber and Prairie Areas 76 

64. Soil Samplers 119 

65. Bottle for Subsidence Method of Mechanical Analysis 125 

66. Nobel's Elutriator 126 

67. Schone's Elutriator 126 

68. Hilgard's Churn Elutriator 126 

69. Machine for Centrifugal Analysis of Soils 127 

70. Yoder's Centrifugal Elutriator 127 

71. King's Aspirator for the Determination of the Effective Diameter of 

Soil Particles 128 

72. Shrinkage of Different Types of SoU 133 

73. Cracks in Black Clay Loam After a Long Dry Period 136 

74. Fragments of Plants Found in Soils 143 

75. Fragments of Insects Found in Soils 143 

76. Specimens of Charcoal and Charcoal-Uke Material Found in Soils 146 

77. Specimens of Coal Found in Soils 146 

78. The Effect of the Removal of Humus and of Wetting and Drying 

Upon Granulation 149 

79. Arrangement of Apparatus for Determining Organic Matter by 

Chromic Acid Method 155 

80. Clover on Gray Silt Loam on Tight Clav 159 

81. How Does This Man Handle Manure? 165 

82. When the Spreader is Filled the Manure is Hauled to the Field 165 

83. Manure Spreader in Action 167 

84. An Expensive and Wasteful Way of Handling Manure on the Farm . 169 

85. Burning Corn Stalks 170 

86. Adding Organic Matter to the Soil in the Form of Sweet Clover 172 



ILLUSTRATIONS xi 

87. A. Showing Angular Character of Quartz Particles in Decomposed 

Gneiss. B. Quartz Granules from Beach Sand. C. Showing 
OutUnes of Shreds of Volcanic Dust as Seen Under Microscope . 179, 180 

88. Diagram Showing the Arrangement of Soil Particles 180 

89. The Annual Rainfall Over the United States 190 

90. Soil Particles Showing Films and Waists of Capillary Water 200 

91. Large and Small Bubble Connected by a Tube 200 

92. Showing Theoretically the Thickness of Films in a Vertical Soil 

Column 201 

93. Showing the Effect of Various Amounts of Organic Matter on the 

Rise of Capillary Water from a Free-water Surface for a 14-day 
Period 208 

94. Diagram Showing the Relation of Different Forms of Moisture to the 

Available and Unavailable Moisture of Soils 214 

95. The Difference in Germination and Growth on Undrained and 

Drained Soil 223 

96. Pipe Heaved Nearly 6 Inches During Winter of 1915-1916 225 

97. Alfalfa that was Completely Killed by Heaving. 226 

98. The Obstructions Interfere with the Current and Cause Deflections . . 227 

99. Ditch Gradually Being Filled by Soil Due to Current Being Retarded 

by Grass 227 

100. A Neglected Ditch Often Seen in Heavily Wooded Areas 227 

101. Showing the Water Table with Lines of Tile Soon After the Insertion 

of Another Lme 228 

102. A Good Method of Conserving Moisture 234 

103. Types of Rainfall Over Dry-farm Area of the United States 239 

104. Sage Brush on Land Well Adapted to Dry Farming. Utah 239 

105. A Gravelly Soil Not Well Adapted to Dry Farmuag 240 

106. A Deep, Medium-gramed Soil Well Adapted to Dry Farming. Utah. 243 

107. Campbell Subsurface Packer 247 

108. Turkey Red FaU Wheat, Without Irrigation, Yield 58 Bushels Per 

Acre 249 

109. White HuUess Barley on Land Continuously Cropped 249 

110. W^hite HuUess Barley on Land Fallowed the Previous Year 249 

111. Corn Grown on Dry-land Farm. Utah 252 

112. Dry-farm Potatoes. Utah 253 

113. Conduit for Conducting Water to Where it May be Used for 

Irrigation 258 

114. Concrete- lined Canal that Permits no Loss by Seepage 258 

115. Roosevelt Dam, Salt River, Arizona 260 

116. Granite Reef Diversion Dam, Salt River Project, Arizona 260 

117. Desert Lands and Homestead, Huntley Project, Montana 261 

118. Wheat Field, Minidoka Project, Idaho 261 

119. Chains for Puddling the Mud of Canals to Prevent Seepage 267 

120. Rectangular Weir 268 

121. Trapezoidal or Cippoletti Weir, Showing Method of Dividing the 

Stream 269 

122. Basin or Check System of Irrigating Orchards 270 

123. Irrigating Potatoes by Furrows 271 

124. Method of Irrigating by Overhead Sprays 272 

125. Mallin Ranch, Salt River Project, Arizona 274 

126. Alfalfa Field, Yuma Project, Arizona 274 

127. Beginning of an Alkali Spot '. . . . 279 

128. Alkali Area Showing the Absence of Vegetation 279 

129. Apricot Trees. The Scanty Foliage Shows the Effect of Alkah 283 

130. An Orchard Well Cultivated Prevents the Rise of Alkali 286 



xii ILLUSTRATIONS 

131. Growth of Barlev on Partly and FuUv Reclaimed Alkali Land 28S 

132. Wheat on Reclaimed Alkali Land Near Fresno, Cal 289 

133. A Dwarfed Bushy or Leafy Corn Plant Growing on Alkali Soil of 

Humid Area 291 

134. DitTerence in Growtli on Light and Dark Colored Soils 303 

135. Showing the Comparative Areas Covered bv the Sun's Rays When 

Vertical, 30, GO and SO Degrees from the Vertical 304 

136. Effect of Slope on the Area Covered by the Sun's Rays 305 

137. Diagram Showing the Theoretical Action of the Plow 327 

138. Showing the Three Types of ^lold-boards 327 

139. Plow with Separate Jointer and Rolling Coulter Attached Readv for 

Use '. ... 328 

140. The Combined Jointer and Rolling Coulter 329 

141. Disk Plow 329 

142. Lister for Preparing the Ground and Planting Corn 330 

143. Work Done bv Lister 331 

144. Stibsoil Plow." 331 

145. Spike-tooth Harrow 332 

146. Spring-tooth Harrow 332 

147. Acme Blade Harrow 333 

148. The Solid Disk 333 

149. The Cut-away Disk 334 

150. The Spading Disk Harrow 334 

151. Smooth or Driun Roller 335 

152. The Culti-paeker, a Form of Corrugated Roller, Showing Work Done 336 

153. Disk Drill and Its Work 336 

154. Press Drill 337 

155. Ordinary Corn Planter with Attachment for Planting Cowpeas in 

Hili or Row with Corn 338 

156. Three-shovel Cultivator 338 

157. Disk Cultivator 339 

15S. Siuface or Blade Cultivator with Leveler 339 

159. Weeder 340 

160. An Early Form of Plow 340 

161. The Sod is Well Turned and Represents Good Work 341 

162. Good Plowing in Stubble Land 342 

163. A Crooked Furrow Does Not Look Well 342 

164. l\evious to Plowing. Disking Should be Done 344 

165. Grain Produced from Five Tenth-acre Plots Prepared in Different 

Ways for ^^"inte^ Wheat 346 

166. A Good Seed Bed on Stalk Grotmd 348 

167. Nine-year Average Yield 43.3 Bushels Per Acre 351 

168. Nine-year Average Yield 4S.9 Bushels Per Acre 351 

169. Nini^vear Average Yield 7.4 Bushels Per Acre 351 

170. Yields of Corn (Field Weight "i with Different Methods of Tillage. . 354 

171. Yield of Corn (Fiold Weight^ with Different JNIethod of Tillage. ... 354 

172. Level Cultivation 355 

173. Ridged. Cultivation with Drilled Corn 356 

174. Two Htmdred Square Miles of Once Forested Mountains in China . . 359 

175. Sweet Clover on Badly Eroded Land. 361 

176. Cultivated Terraces in China 364 

177. Gttide-row Terraces 365 

17S. Level-bench Terrace ." 366 

179. A Terraced Park in Mississippi 367 

180. The Mangum Terrace 367 

181. Locusts Growing on Gullied Land 368 



ILLUSTRATIONS xiii 

182. Erosion in Pasture Near Crest of Slope 370 

183. Old Field Erosion in Mississippi 370 

184. Old Erosion 371 

185. Brush Checking Erosion 372 

186. Headwater Erosion 372 

187. Earth-dam for Checking Erosion 372 

188. Fillmg a Gully bj^ Means of a Concrete Dam 373 

189. Agricultural Provinces 383 

190. Wheat Growing on a Soil Very Deficient in Nitrogen 397 

191. Legumes Turned Under Have the Same Effect as the Addition of 

Nitrogen 397 

192. "\Mieat, 1911, Urbana Field 401 

193. Wheat, 1911, Urbana Field. Finely Ground Rock Phosphate 

AppUed 401 

194. Corn on Peaty Swamp Land, 1903 404 

195. Farm Land, Value Per Acre, 1910 410 

196. Fami Propertv, Value, 1910 411 

197. Corn Acreage, 1909 412 

198. Corn Production, 1909 413 

199. Oats Production, 1909 414 

200. Sprina- \Mieat Acreage, 1909 415 

201. Winter Wheat Acreage, 1909 416 

202. Wheat Production, 1909 417 



SOIL PHYSICS AND 
MANAGEMENT 

CHAPTER I 
SOIL MATERIAL AND ITS ORIGIN 

Definition of Soil. — The land surface of the earth is covered 
almost everywhere with a layer of unconsolidated material de- 
rived from .rocks by the processes of weathering. This stratum 
varies in thickness from a few inches to hundreds of feet and may 
even be absent from small areas, not because it was never formed 
there, but because it has been carried away. The agencies of trans- 
portation have done so much work that in many instances much 
or all of the loose material covering the rocks was not derived 
from those beneath, but from rocks at some distance, even hundreds 
of miles awa}'. This material varies in composition with the rock 
from which it was derived and the agencies producing it. It cannot 
I)e termed a soil until organisms have worked upon it, modifying 
it to a greater or less extent. The depth of the layer upon which 
the organisms have acted is only a few feet. 

From its origin, a soil may be defined as disintegrated and 
decomposed rock mixed with more or less organic matter, while 
from its use it is defined as that part of the earth's surface adapted 
to the- mechanical support and nourishment of plants. 

Elements of the Earth's Crust. — The earth has been studied 
by various means and the composition determined to ' a depth of 
approximately twenty miles. Of the elements known, comparatively 
few occur in any large quantities in this stratum. Eight constitute 
about 98.5 per cent. The following table shows the relative abun- 
dance of these elements. 

Soil Forming Minerals. — Aside from oxygen and nitrogen as 
air, and carbon as graphite or diamond, these elements rarely ever 
exist in a free state, but are found in combinations as minerals. 
These are natural substances, possessing definite physical charac- 
teristics as, specific gravity, hardness, brittleness. color, cleavage, 
and sometimes crystalline form and having a more or less definite 
chemical composition. 

1 



SOIL PHYSICS AND MANAGEMENT 

Average Composition of the Knovm Earth ^ 



Elements 


Lithosphere f 
93 per cent 


Hydrosphere J 
7 per cent 


Average, 

including 

atmosphere 


Oxveen * 


47.33 

27.74 

7.85 

4.50 

3.47 

2.24 

2.46 

2.46 

.22 

.46 

.19 

.06 

"".12 
.12 
.08 
.08 
.02 

' " ' !l6 

.50 


85.79 

' ' .05' 

.14 

1.14 

.04 

10.67 

'.002 
2.07 
.008 

' " '.09' 


50.02 


Silicon 


25.80 


Alnniimim 


7.30 


Iron 


4.18 


Cfllr.hiTTi 


3.22 


Magnesium 


2.08 


Sodium 


2.36 


Potassium 


2.28 


Hydrogen 


.95 


Titanium 

Carbon 


.43 

.18 


Chlorine 


.20 


Bromine 


" .ii 


Sulf xir 


.11 


Manganese 


.08 
.08 




.02 


Nitrogen 


.03 




.10 


All other elements 


.47 








100.00 


100.00 


100.00 



* The elements essential for crops are in bold tj-pe. 
t The solid part of the earth's crust. 
J The liquid part, oceans, seas, etc. 

The hardness of miuerals is indicated by the following scale: 
(1) talc — finger nail scratches it easily; (2) gypsum — thumb nail 
scratches slightly; (3) calcite — can be scratched by common soft 
pin; (4) fluorite — soft iron scratches it; (5) apatite — scratched 
by a good knife; (6) feldspar — very hard knife scratches it; (7) 
quartz — scratches glass; (8) topaz — scratches quartz; (9) corun- 
dum — scratches topaz ; (10) diamond. 

The number of minerals that form soils is not large, but they 
may be found in many intermediate stages because the process of 
decomposition is a gradual one. 

1. Quartz, silica (SiOo) is a very abundant mineral in rocks 
and the most abundant in soils. When crj'stalline it possesses a 
glassy appearance and is transparent in thin slices, but impurities 
render it more or less opaque. The common crystalline varieties 
are quartz crystal, rose, smoky and milky quartz. The non-crys- 
talline varieties are usually opaque and include flints, cherts, 
chalcedony and the different forms of agate. In rocks such as 



SOIL MATERIAL AND ITS ORIGIN 



granite, quartz occurs as glassy masses wliich do not decompose as 
most other minerals do, but remain as distinct grains of quartz 
when the rock is broken down. In limestones it frequently occurs 
as chert, an impure rather soft form, or as flint. Sand, sandstones, 
and quartzite are formed principally of quartz. The fact that its 
hardness is 7, that it is almost insoluble, decomposes very slowly and 
possesses no cleavage, makes it very abundant among the coarser 
constituents of soils. It may be distinguished by its glass-like ap- 
pearance, hardness, shell-like fracture, lack of cleavage and its 
resistance to the action of all acids with the exception of hydro- 
fluoric. 

2. Feldspars. — ^The feldspars include double silicates of potas- 
sium, sodium, calcium and aluminum. They possess a hardness of 
6, distinct cleavage and decompose rather readily in the presence 
of carbonated water. The action of carbonic acid is to dissolve 
out the base or bases, forming the soluble carbonates, leaving a 
hydrated aluminum silicate, kaolin, and finely divided free silica 
which constitute the clay of soils. The process is known as kaolin- 
ization. The following table gives the composition of the principal 
feldspars. 





Composition of Principal Feldspars ^ 
Per cent 






Varieties 


Si02 


AI2O3 


K2O 


NazO 


CaO 


Orthoclase 

Albite 

Oligoclase 

Labradorite 

Anorthite 


64.7 

68.0 

; 62.0 

t 53.0 

43.0 


18.4 
20.0 
24.0 
30.0 
37.0 


16.9 


i2!o 
9.0 
4.0 


'5!o 

13.0 
20.0 



As an illustration of the decomposition of feldspar, orthoclase 
may be taken. Carbonated water coming in contact with this min- 
eral dissolves out the potassium, forming potassium carbonate, which 
being soluble is carried away. In the process the excess of silica 
which amounts to approximately 20 per cent in orthoclase is sepa- 
rated as extremely fine particles most of which are classed as clay. 
The alumina is left in combination with silica as a hydrous alumi- 
num silicate forming the mineral kaolin which also constitutes clay. 
The result then of the decomposition of feldspar is a light-colored 
clay composed of free silica and kaolin. 

3. Amphibole and Pyroxene. — These groups of minerals are 



4 SOIL PHYSICS AND MANAGEMENT 

very abundant in some rocks and vary a great deal in composition 
and physical properties. They have about the same hardness as 
feldspar and possess more or less definite cleavage planes. They 
may be either aluminous or non-aluminous. Magnesium, calcium 
and iron are nearly always present. The iron is frequently in the 
ferrous condition. x4.s a general rule these groups of minerals 
decompose somewhat readily, giving rise to hydrous magnesium 
silicates and soluble carbonates, the latter of which are carried away 
in solution. The hydrous magnesium silicate may be in the form 
of serpentine or talc, the latter of Avhich, because of its softness, is 
readily broken down into clay. The ferrous iron present becomes 
oxidized and generally gives a yellow or brownish color to the soil 
formed. As these groups of minerals are frequently magnesian, the 
soil resulting is not generally highly productive. 

■i. Muscovite — White Mica. — This mineral is made up of 
transparent laminas or folia possessing a hardness of 2 to 2.5. These 
folia are thin, elastic and tough. 

The chemical composition and physical properties of this min- 
eral seem to indicate that it would decompose rather readily, but 
on the other hand it is very stable and resists decomposition so 
well that in most cases the mica remains in the residue as distinct 
shining flakes, giving the soil a peculiar glittering appearance 
where the flakes are of considerable size. The first step in its de- 
composition is hydration, resulting in a hydrated mica having a 
pearly luster. When decomposition is complete the product is the 
hydrous aluminum silicate or clay. Muscovite is found in granites 
to a considerable extent, but is not very often associated with the 
more basic rocks or those containing a large per cent of magnesium, 
calcium or iron. 

5. Biotite — Black Mica. — Biotite differs from the preceding 
mica in color, and in the fact that it decomposes more readily. It 
contains aluminum and iron in both ferrous and ferric states with 
both magnesium and potassium. It decomposes into a mixture of 
hydrated aluminous and magnesian silicates, both of which con- 
stitute clay. Biotite occurs associated with the more basic rocks. 

6. Zeolites. — The zeolites comprise a group of secondary min- 
erals of somewhat doubtful importance, whose function, it is be- 
lieved, is to retain the potassium and calcium in the soil against 
leaching. In the decomposition of mi]:ierals to form soil material 
the potassium, sodium and calcium unite with the aluminum and 
silica in loose combinations instead of being carried away in solu- 



SOIL MATERIAL AND ITS ORIGIN 5 

tion and. lost. From these combinations tlie elements are liberated 
somewhat as needed by plants. The minerals of this group are de- 
composed by hydrochloric acid with the separation of colloidal 
silica. 

The preceding minerals are silicates, but there are a few non- 
silicates that should be considered in the study of soils. 

7. Calcite (CaCOg). — Calcite is a very common mineral exist- 
ing as limestone and marble. Its composition is CaO, 56 per cent, 
and COo, -i-l per cent, when pure. It possesses a hardness of about 
3, distinct cleavage and is soluble in carbonated water, one part in 
1020 of water, forming the bicarbonate {CalioiCOs)^). In the 
formation of soil material from rock made up largely of calcium 
carbonate, the insoluble impurities are left and form the soil. As a 
general rule limestone soils are quite fertile. 

8. Dolomite (CaMg(C0o)2).— The hardness of dolomite is 3.5. 
It is composed of 5-±.35 per cent of calcium carbonate and 45.65 per 
cent of magnesium carbonate. Dolomitic limestone is made up of 
these minerals, though probably not always in these proportions. It 
is slowly soluble in carbonated water, leaving the impurities to form 
soil material. A large amount of magnesium carbonate is injurious 
to some crops and constitutes much of the alkali in soils of humid 
areas. 

9. Gypsum (CaS04.2H20). — Gypsum possesses a hardness of 
2 and the following composition : sulfur trioxid, 46.5 per cent, lime 
32.6 and water 20.9 per cent. It is found in considerable quantities 
in arid regions where salt lakes formerly existed, but is of compara- 
tively little imjjortance as a soil former, since the soil derived from 
it has very little value. It has, however, some value as a remedy 
for black alkali that is so frequently found in arid and semi-arid 
regions. 

10. Apatite (Ca-(P04)3C1). — This mineral is important in 
soils because of the phosjahorus it furnishes. Fortunately it exists 
in all rocks, though in very small amounts, and when these decom- 
pose very little of the phosphorus is lost through solution. Hence 
a soil will usually show a higher per cent of phosphorus than the 
original rock. In some cases the chlorine is replaced by fluorine. 

11. Limonite (2Feo03.3HoO) and Hematite (FeoOg).— Sev- 
eral other minerals might be mentioned, among which are limonite, 
the hydrated ferric oxide having 85.6 per cent of FcjOg and 14.4 per 
cent of water, and hematite 30 per cent of oxygen and 70 per cent, 
of iron. One or the other of these and sometimes both are found in 



6 SOIL PHYSICS AND MANAGEMENT 

nearly all soils giving the characteristic iron color, the former im- 
parting a 3'ellowish or brownish yellow color while the latter gives 
a decidedly reddish color. Varying proportions of these mixed 
together give many shades of red, brown and yellow. 

12. Magnetite (FegO^) or (FeO. FeoO.,). — Magnetic iron ore 
or magnetite exists in nearly all igneous rocks in small quantities 
but in some in sufficient amounts to form a very important soil con- 
stituent. It does not decompose very readily, but remains as black 
magnetic particles in the soil. Black sands of some parts of Xorth 
Carolina and some of the alluvial soils of California contain this 
mineral. It may be easily recognized by its magnetic properties. 
Like quartz sand it is inert- and soils formed largeh' of tliis mineral 
would be very poor. 

ROCKS 

Eocks are masses of minerals or mineral aggregates and are 
divided into three classes, igneous, those formed through the agency 
of heat, aqu-eous. those formed through the agency of water, and 
metaniorpJiic, where igneous or aqueous rocks are changed through 
one or both of tliese a.gencies into different forms, but having prac- 
tically the same chemical composition. 

1. Igneous rocks are divided into two groups, first, ■intru- 
sive or pJutonic, those formed at considerable depth in the earth's 
crust where they cooled with sufficient slowness to crj-stallize, and 
later exposed through erosion; second, eruptive or volcanic, those 
thrown out on the surface of the earth through volcanic agencies. 
Both classes of igneous rocks are formed by the fusing and mixing 
of rocks, such as limestones, shales and sandstones, due to the heat 
developed in the folding of the earth's crust in its adjustment to 
the shrinking interior. After the adjustment takes place, this 
molten mass gradually cools, the minerals crystallize, forming the 
group of crystalline rocks. In this folding, if a fracture should 
occur extending to the surface of the earth, much of this molten 
mass may be forced out on the surface and constitute the volcanic 
rocks. This may cool rapidly and solidify into a glassy or semi-crys- 
talline condition. In some cases the violence of the explosion that 
frequently accompanies volcanoes throws immense masses of this 
material into the air which falls in the form of ash in the vicinity 
of the volcano, but sometimes as dust is carried over large areas of 
the earth's surface by air currents. The igneous rocks are divided 
into several groups according to their mineral composition. 



SOIL MATERIAL AND ITS ORIGIN 7 

(a) Granite-Rhyolite. — This group is composed of quartz, 
feldspars, chieliy ortlioclase and albite, mica, either black or white, 
and amphibole or pyroxene. A small amount of apatite is always 
present. Khyolite is the principal volcanic rock of this group. In 
the decomposition of this group carbonated water attacks the feld- 
spars, dissolving out the potassium and sodium in the form of car- 
bonates, leaving the clay residue. The quartz is broken down into 
sand and gravel while the other minerals are decomposed into other 
products as given under those special minerals above. ■ The resulting 
soil material formed is a sandy clay, the color depending upon the 
amount of iron-bearing minerals in the granite. The soil material 
formed from rhyolites and other volcanic granites differs only in 
fineness from that resulting from intrusive granites. 

(b) Syenite-Trachyte. — This group consists chiefly of the 
feldspars, orthoclase or albite, minerals of the mica, amphibole or 
pyroxene groups and a small amount of apatite. It differs from the 
granites in the absence of quartz. Its decomposition is similar to 
that of the granite but gives a clay free from sand, colored by iron 
compounds. This rock is not so common as granites. Trachyte is 
the volcanic form of syenite. 

(c) Diorite-Andesite. — These rocks contain oligoclase, mica, 
usually biotite, amphibole or pyroxene and apatite. Quartz may 
be present. The soil material formed is either a rather highly 
colored clay or sandy clay, depending on the absence or presence of 
quartz in the original rock. Andesite is a common volcanic form. 

(d) Diabase-Basalt. — This group of rocks consists of labrado- 
rite, amphibole or pyroxene, usually the latter, and small amounts of 
apatite. Quartz may be present in small quantities as in the case of 
the diorites. Usually large amounts of magnesium and iron-bearing 
minerals are present. The decomposition of this group gives a 
highly colored clay containing large amounts of hydrated mag- 
nesium silicates. Basalt is the volcanic form. 

Other groups of igneous rocks might be given, but these are 
sufficient to illustrate the changes that take place in the formation 
of soil material from them. 

2. Aqueous rocks are divided into three classes, (a) those 
whose constituents have been in solution and have been deposited 
b}"- cooling, evaporation, release of pressure or by direct chemical 
precipitation; (b), sedimental or fragmental deposits, those formed 
by the breaking down of preexisting rocks and deposited by the 
action of water; and (c), those formed largely by plants and 



8 SOIL PHYSICS AND MANAGEMENT 

animals. It is quite impossible to draw any distinct lines between 
the groups. 

(a) Chemical Precipitates. — Eocks formed in this way are not 
of a great deal of importance as soil formers, but have great eco- 
nomic value. These include the precious stones, the ores both of 
useful and precious metals and deposits of plant food, especially 
potassium and phosphorus. 

(b) Sedimentary or Fragmental. — This division includes 
sandstones and shales. Saiidsfones may be divided into classes ac- 
cording to the material that cements the particles together, as 
siliceous, ferruginous, or calcareous. Siliceous sandstones break 
down largely through physical or mechanical agencies, forming a 
sandy soil of unusually low agricultural value. A good example of 
this is the St. Peter's sandstone of northern Illinois. Ferruginous 
sandstones are broken down in a way similar to the siliceous, except 
that chemical agents are more apt to affect the cementing material. 
The resulting soil is a sand, colored by compounds of iron and does 
not possess a high degree of fertility. In the breaking dowai of 
calcareous sandstones, the lime is dissolved out by the action of 
carbonated water, thus freeing the particles and forming a rather 
poor sandy soil. The decomposition of felspathic sandstones may 
give rise to soils of fair fertility because- of the potassium and lime 
present, but on the other hand micaceous sandstones produce soils 
of low value. 

Shales vary largely in physical composition. Some are composed 
of clay while others contain much coarser material, such as silt or 
even sand. The indurated character of shales is principally due to 
pressure and they are consequently easily broken down into soil 
material. The stratification also aids this process. The soils formed 
from shales vary from very heavy clay to silty or sandy ones, and 
may be extremely difficult to work. In general shale soils are not 
of high agricultural value. 

(c) Organic.^ — This includes those deposits that have been 
formed through the agency of organisms. They consist of coal, 
chalk, marl, and limestone. 

Calcareous rocks include chalk, marl, and the various limestones 
(Fig. 1.) Soils are formed from these through the solvent power of 
carbonated water which removes the lime and magnesia as the 
bicarbonate, leaving the insoluble impurities as soil material. This 
may consist of particles of sand or quartz or some of the finest soil 
constituents as silt or clay (Fig. 2). Limestones frequently con- 



SOIL MATERIAL AND ITS ORIGIN 



tain masses of chert, impure quartz, or flint which may constitute 
no small part of the soil, thus giving rise to cherty or flinty soils. 
The rapidity with which a soil is formed from a limestone depends 




Fia. 1. — Limestone composed chiefly of shells of Brachiopods. (Church.) 




Fig. 2. — Limestone containing large amounts of Crinoid stems. (Church.) 

upon the amount of impurities present. A limestone containing 
two per cent of impurities could leave approximately two feet of 
residue for each 100 feet of limestone removed in solution provided 
nothing is lost by erosion. Limestone soils are usually fertile. 



10 SOIL PHYSICS AND MANAGEMENT 

3. Metamorphic rocks iuelude those tluu have heeu changed 
from their original condition by both physical and chemical agen- 
cies. These may have been of either aqneons or igneous origin. 
Changes have given rise to marbles from limestones, slates from 
shales, and gneisses and schists from igneous rocks. 

QUESTIONS 

1. Detine soil. 

2. Which of the elements essential for crops are taken from the air ami 

which from the soil? 

3. What is the signiticanee of the luirdness of a mineral in the formation of 

soils? 

4. Why should quartz be such a common constituent of soils? 

5. Why is little feldspar found in soils when it is so abundant in rooks? 
0. What is the chief value of zeolites? 

7. What is the importance of non-silicates as soil formers? 

S. Which are the principal non-silicate minerals in soils of luuuid regions? 

9. How are igneous rocks formed ': 

10. Give distinctions between granite's, svenites. diorites, and diabases. 

11. Distinguish between chemical precipitates and seilimentary rocks. 
1"2. How are soils formed from calcareous rocks? 

13. Where do we find soils formed from chalk? From limestone? 

REFERENCES 

^ Clark. F. W., Bulletin (UO U. S. Geological Survey. The Data of Geo- 

chemistrv, iSUii. p. 34. 
* Merrill, G. P.. Kocks. Eock-Weathering and Soils. 1906, p. 15. 



CHAPTEE II 

WEATHERING 

EocKS are broken down into soil material throngh the processes 
of weathering (Figs. 3, 4, and 5). These may be divided into (1) 
physical agencies that break the rock into smaller pieces without 
affecting it chemically, and (2) chemical agencies that change the 
composition of the minerals forming the rock and in so doing exert 




Fig. 3. — Irregular weathering of rock due to Joints and stratification. Note talus at base. 
(Chamberlain and Salisbury, Courtesy Henry Holt & Co.) 

a marked influence upon its physical character. The work of the 
physical agencies is disintegration, while that of the chemical agen- 
cies is decomposition. Each is accompanied and aided by the other 
in its work and the changes tend to produce more stable forms under 
existing conditions. As an illustration, feldspars are not very stable 
minerals under ordinary conditions, and hence break down into 
substances that are more stable. The chemical changes produce 
hy^drous aluminum silicate, carbonates and free silica which are 
much more stable than the feldspar from which they are derived. 
Physically, the clay is much more stal^le than the original mineral 

11 



12 



SOIL PHYSICS AND MANAGEMENT 



or even the coarse soil coustitueiits because it has approached more 
closely the limit of mechanical division. The others may be broken 
down into smaller fragments by the agencies of weathering. 




Fig. 4. — A more advanced stage of weathering than Fig. 3. (Chamberlain and Salisbury, 
Courtesy Henry Holt & Co.) 




Fig. 5. — "Capitol K.hI 



, Montana. The different levels are due to varying hard- 
uloo of the rock strata. 



I. niYSICAL AGENCIES. 

(a) Heat and Cold. — In general, substances expand Avhen 
heated and contract when cooled. This is true of rocks. They are, 
however, poor conductors of heat and the high temperature of the 



WEATHERING 



13 



rock extends to only a slight depth. The greater expansion of the 
surface produces a strain that frequent!}^ causes a layer to break off, 
sometimes with considerable violence (Fig. 6). In Lower Cali- 
fornia, slabs as much as ten feet long and from eight to ten inches 
thick have been obsen-ed on the southwest side of rock exposures 
that were produced in this way. j\Iany similar cases may be seen in 
the arid regions in southwestern United States. Boulders are some- 
times found in this latitude that show peculiar exfoliation due to 
unequal heating. This action is more noticeable in fine-grained 




Fig. 6. — Exfoliated granii. iii m^ Sierra Nevadas, California. Previous glaciation 
has removed the loose material, giving the agency of heat a better chance. Rocks, Hock- 
Weathering and Soils, Merrill. (Courtesy The Macmillan Companj-.) 

than in coarse-grained rocks, and in higher altitudes where the tem- 
perature changes are great and sudden. "W. H. Bartlett ^ has shown 
that granite expands or contracts .0000048 of an inch per foot for 
each degree Fahrenheit. Marble changes .0000056, while sandstone 
changes .0000095 of an inch per degree. Practical applications of 
this principle have sometimes been made in quarrying and in re- 
moving rocks in constructing roads. Boulders may be broken up by 
heating and cooling suddenly. Eocks are made up of various min- 
eral crystals that possess different coeflicients of expansion. The 



14 



SOIL PHYSICS AND MANAGEMENT 



repeated differential expansion and contraction of adjacent unlike 
minerals due to temperature changes of day and night loosen the 
crystals, causing the rock to crumble. This plays a more prominent 
part in the breaking down of coarse- than fine-grained rocks. In this 
way rocks are weakened and finally reduced to soil material by 
other agencies. 

(b) Freezing and Thawing. — When water passes from the 




Fig. 7. — Columbia Glacier overriding a forest, Alaska. (Courtesy National Geographic 
Magazine, Washington, D. C. Copyright.) 

liquid to the solid condition its volume is increased by about nine 
per cent, and the force exerted is 150 tons per square foot, or over a 
ton per square inch. Water frequently freezes under conditions such 
that part of this force is used in enlarging crevices in rocks, break- 
ing off small fragments or displacing masses to such an extent that 
when thawing occurs they may roll down the slope. This is espe- 
cially noticeable during a morning thaw on stony slopes free from. 



WEATHERING 



15 



vegetation. Very porous rocks are frequently disintegrated rapidly 
by freezing, especially when the rocks approach saturation. Eocks 
possessing vertical joints or made U23 of inclined strata of different 
material will weather rapidly because of greater absorption of water. 
This action does not occur in tropical or subtropical climates, but in 
temperate regions it is very important in breaking down rocks and 
in keeping the subsoil open so that both air and water may enter the 
soil much more readily and carry on their work to a greater extent 
upon the underlying rocks. 




Fig. S. — Front of Coluniliia Cilacier in 1910 compared in height to Bunker Hill Monument. 
The pinnacle fell a few minutes after the picture was taken. (Lawrence Martin.) 

(c) Glaciers. — At the present time the work of glaciers is lim- 
ited to a comparatively small area of the earth's surface (Figs. 7 
and 8). During the glacial period about half of ^N'orth America 
and Europe were covered ^^dth an ice sheet, and the work of this 
agent was very important in that it leveled hills and filled valleys, 
ground up and deposited large amounts of fine soil-forming mate- 
rial. This deposit is found not only on the glaciated areas, but was 
carried far beyond the ice sheet by water and further distributed by 
the wind. Glacial areas are now confined to polar and a few moun- 
tainous regions. Greenland with an area of 500,000 square miles is 



16 



SOIL PHYSICS AND MANAGEMENT 



almost entirely covered by au ice sheet. This approaches somewhat 
the condition that existed over North America and Europe during 
the glacial period. 

Glaciers are drainage systems of regions of perpetual snow. The 
moving ice obeys the same laws as streams and does the same kind 
of work, but the fact that ice is a solid body gives it great grinding 
power. Ice exerts a pressure of forty pounds per square inch for 
every one hundred feet in thickness, and geologists estimate the ice 
to have been from a few hundred to five thousand feet or more in 
thickness during the glacial period. This great pressure gives the 
ice immense denuding and grinding power. Glaciers move from a 
few feet to one hundred feet per day, the movement being more rapid 




FiG. 9. — The material carried and rolled by streams gives them their great eroding po-ner. 
(U. S. Reclamation Service.) 

in summer. In their movement large masses of rock become im- 
bedded in the bottom of the glaciers, grooving and grinding the 
solid rock over which they pass. It must be remembered, however, 
that the ice did not hold these rigidly. 

(d) Erosion of Streams. — Flowing water doubtless is the most 
extensive physical agent in the formation of soil material at the 
present time. The streams with their load of clay, silt, sand, gravel, 
and even boulders are not only using these tools to deepen and widen 
their valleys but they also grind the materials into powder fitted for 
soil formation. The work of moving water varies as the square of 
the velocitv- If the velocity is doubled the work that the stream is 
capable of doing will be increased four times, since by doubling the 
velocity, twice the number of particles will strike an object with. 
double the force. The deepening and widening of the stream chan- 



WEATHERING 



17 



nel is due mainly to the mechanical wear or friction of the material 
carried by the water (Fig. 9)- Clear water abrades very slowly. 
A rapidly flowing stream carrying large amounts of material abrades 
its bed very rapidly. This may be illustrated in the valleys that 
have been cut by streams that contain water only after very heavy 
rains. Level plateaus have been dissected and changed into a rugged 
country of hills and valleys by comparatively small wet weather 
stream's. The entire land surface has been greatly modified by this 
process and the transported material used largely in soil formation. 




Fig. 10. — Inner gorge of Grand Canon of the Colorado River, Arizona. (Waleott, IT. S. 

Geol. Survey.) 

Captain C. E. Button ^ estimates that 10,000 feet of rock strata 
have been removed from an area of 13,000 to 15^000 square miles 
by the Colorado Eiver (Fig. 10). 

When quartz is ground up through the action of moving water 
much sand is produced, and after these particles have been reduced 
to a certain size the permanent water film protects them largely from 
further attrition. On the other hand, feldspars when suljjected to 
attrition form an impalpable mud or clay accompanied by consider- 
able loss of bases such as potassium, sodium, or calcium, according 
to the kind of feldspar. 
2 



18 



SOIL PHYSICS AND MANAGEMENT 



(e) Waves. — Wave action is confined to the shores of seas and 
the larger lakes. In many places this agency breaks down solid cliffs 
into masses of rock that become broken and worn into rounded 
boulders, then to pebbles, and finally into fine material that is car- 
ried away and deposited in deejDer water or in sheltered inlets to 
form bars. On the Atlantic coast of Britain waves sometimes exert 
a pressure of three tons per square foot. The average force is 611 
pounds per square foot in summer and 2086 pounds in winter. 
Each wave results in the movement of more or less material, and 




Fig. 11. — ^Wind-carved granite. The tools were grains of sand. Camps Bay, S. Africa. 
(Chamberlain and Salisbury, Courtesy Henry Holt & Co.) 

this movement is accompanied 1)y attrition producing fine material. 
Shaler has observed that at Cape Ann, Mass., granitic paving blocks, 
weighing about twenty pounds, when exposed to the action of the 
surf for a year, were worn into spheroidal boulders that would indi- 
cate a loss of more than an inch. 

(f ) Wind. — The movement of wind is universal, but its effect 
is destroyed or greatly reduced, at least, at certain seasons of the 
year over large areas o'f the land surface by the covering of vegeta- 
tion. Along the coasts, in the arid interiors of continents, and 
during winter and spring in many areas, a large amount of work is 



WEATHERING 



19 



done by the wind in wearing down solid rocks and coarse soil mate- 
rials into dust. The impact of sand particles against rocks and 
against each other gradually wears them down into fine materials 
(Fig. 11) . The largest ntmiber of particles are moved near the sur- 
face of the ground, hence the greatest amount of abrasion will take 
place there. A boulder will be worn away slowly on the mndward 
side at the base until it topples over, and the process will then be 
repeated until it is entirely destroyed. Along shores the glass in 
windows of houses is sometimes worn through by the iiiip.icf of 
sand particles, and an instance is 
given by Merrill ^ where the glass in 
a lighthouse was ruined during a sin- 
gle storm. Sand blasts are used to 
jDroduce ground glass. The natural 
monuments and " mushroom " rocks 
in the West owe their origin largely 
to the work of the wind. 

(g) Plants. — The mechanical 
action of plants is shown by the 
growth of roots in crevices or fissures 
of rocks and the prying apart of great 
masses, thus giving other agencies 
an opportunity for effective work. 
The force exerted by mushrooms or 
toadstools is sometimes sufficient to 
raise blocks of stone, while cement 
walks are frequently ruined by the 
lifting action of roots of trees grow- 
ing adjacent (Fig. 12). Hilgard* 
makes this statement, " Actual meas- 
urement has shown the force with which the root, e.g., of the garden 
pea penetrates, to be equal to from seven to ten atmospheres per 
square inch." 

II. CHEMICAL AGENCIES. 

(a) Acids. — The atmosphere in all localities contains more or 
less acid gases, which in combination with the moisture of the air 
form acids that are brought down with the rain. These acids are 
much more abundant in the vicinity of manufacturing plants, smel- 
ters, and large cities where they are produced, largely by the burning 
of coal. Sulfuric acid is probably the most common of these and 




Fig. 12. — The roots of trees form 
wedges for prying rocks apart. (Gil- 
bert, U. S. Geol. Survey.) 



20 SOIL PHYSICS AND MANAGEMENT 

contributes much toward the breaking do\\Ti of rocks. Nitric acid is 
formed under certain conditions in the atmosphere, and, although 
the amount reaching the surface of the earth per acre per annum is 
small, amounting at Eothamsted, England, to from 2.81 pounds to 
2.98 pounds, yet the long-continued action of this acid during geo- 
logical time has done a great deal toward breaking down rocks into 
soil material. In some localities hydrochloric acid forms a very 
active agent, especially upon limestone and marble. 

(b) Carbon Dioxide. — The most effective acid in decomposing 
rocks is that produced by the union of carbon dioxide and water, or 
carbonic acid. Carbon dioxide is found in the atmosphere in all 
localities, but, of course, in slightly greater quantities near cities 
and factories than at other jDlaces. It is considered a weak acid, yet 
because of the fact that it is always present, it exerts an immense 
influence in breaking down rocks, especially those containing lime, 
magnesia, potash, and soda. The soil air contain^ much larger 
amomits of carbon dioxide than the air above, thus percolating water 
becomes highly charged before coming in contact with the rocks 
beneath. Carbonated water is an almost universal solvent. Tlie 
amount of carbon dioxide in air under different conditions is shown 
by the following table: 

Amount of Carbon Dioxide in the Soil Air, and in the Atmosphere ^ 

Parts per million by weight 

Ordinary atmosphere 285 to 600 

Air from sandy subsoil of forest 3,800 

Air from loamy subsoil of forest 12,400 

Air from surface soil of forest 13,000 

Air from surface soil of vineyard 14,600 

Air from pasture soil 27,000 

Air fom soil rich in humus 54,300 

Fischer has shown that in rain and snow water the amount of 
carbon dioxide varies between 0.22 and 0.45 per cent by volume of 
water. These figures according to Merrill would give for the Atlan- 
tic Coast States a depth of 3.75 nmi. of carbon dioxide brought to 
the surface in rain and snow, for the upper Mississippi valley 2.50 
mm., for the lower Mississippi valley 4.50 mm., and for the ]!*^orth- 
ern Pacific States 6.25 mm. Water percolating through soil would 
absorb additional amounts. 

(c) Oxidation. — The only element that free oxygen of the air 
acts upon is iron when in the sulfide or ferrous condition. When 
the iron of the sulfide is oxidized, iron sulfate is formed, which is 



WEATHERING 21 

soon further oxidized so that the hydrated ferric oxide and sulfuric 
acid are produced. The resulting oxide is much softer, more easily 
removed by water and more bulky than the sulfide, hence becomes 
quite absorbent of moisture and is then readily affected by freezing 
and thawing. The expansion produced by the change tends to 
loosen the crystals of the rock and make it very susceptible to other 
agencies. The same is true in the case of iron existing in the ferrous 
condition either as a carbonate or silicate. The resulting products 
of decomposition tend to color the soil material, producing a yel- 
lowish, bro^\alish, or reddish color. 

(d) Deoxidaticn. — I'nder certain conditions oxygen will be 
removed from some compounds, but as a means for breaking down 
rocks this is not very important. The chief agency in deoxidation 
is organic acids. The great affinity of these acids for oxygen enables 
them to take part or all of it from certain compounds, especially 
those of iron, as oxides or sulfates producing a different mineral 
with entirely different physical properties, the n:i,ost noticeable of 
which are color and hardness. In swamps organic acids frequently 
reduce ferric oxides to ferrous oxides and sulfates to sulfides, result- 
ing in a grayish or drab color in the subsoil. The gray subsurface 
and subsoil of many of our poorly drained soils are undoubtedly 
due to the process of deoxidation. The soil under a peat bed is 
usually drab, indicating a reduction of iron. 

(e) Hydration. — During the process of weathering certain of 
the common minerals that compose igneous and metamorphic rocks 
unite with water which not only changes the chemical composition, 
but produces very important changes in the physical character of the 
minerals that aid greatly in breaking them down into soil material. 
This change is usually attended with more or less loss by solution. 
One of the most important changes is the increase in volume, by 
which there is a tendency to rupture the rock. If no loss took place 
by solution, the change of granite into soil through various processes 
of weathering would give an increase in bulk of as much as 88 per 
cent,'^ a large part of which is due to hydration. At the same time 
the hardness of the rock is lowered very materially, and this, of 
course, gives other agencies a better chance. The absorption of 
water will also be increased and freezing and thawing will be more 
effective. The general result of hydration is to render the rock very 
susceptiljle to other agencies. The process of hydration goes on to 
great depth. Apparently solid Imt hydrated rock taken from many 



22 



SOIL PHYSICS AND I^IANAGEMENT 



feet beneath the surface will ermnhle or "" slake *" upon exposure 
to the air. 

(f) Solution. — Water is a universal solvent, but its power is 
greatly increased by the presence of substances in solution so that 
it becomes a very active agent in breaking down rocks. Its elHciency 
is gTeatly increased by the presence of carbon dioxide which is 
absorbed by rain water from the atmosphere and still more from 
the soil air as it percolates through the soil, the air of which con- 
tains large amounts of carbon dioxide. The water thus becomes a 
very active solvent (see table, page 20). 

Effect of Decomposition on Loss of Constituents fi-om Rocks ^ 





Biotite granite, 
Georgia 


Syenite, 
Arkansas 


Diabase, 
^'irginia 


Diorite, 
Virginia 


Limestone, 
Arkansas 




Fresh 
35 feet 
below 
surface 


Decom- 
posed 

5 "-2 feet 
below 
surface 


Fresh 


Decom- 
posed 


Fresh 


Decom- 
posed 


Fresh 


Decom- 
posed 


Fresh 


Resid- 
ual 
clay 


SiOa.-. . . 
AI2O3. . . 
FejOs.. . 

FeO. . . . 
CaO.... 
MgO. . . 
NaoO. . . 
K2O. . . . 
P2O5 . . . 
CO:. . . . 
Ignitio n 
H.,0.... 


69.88 
16.42 

\ 1.96 

J 
1.78 
0.36 
4.46 
5.63 

'6!36 


51.29 
29.69 

6.33 

0.07 
0.14 
1.12 
1.50 

ioise 


59.70 

18.85 

4.85 

*i!34 
0.6S 
6.29 
5.97 

'i.88 


46.27 

38.57 

1.36 

'o;34 
0.25 
0.37 
0.23 

isiei 


45.73 
13.48 

11.60 
9.92 

15.40 
3.24 
0.47 

'6!94 


37.09 
13.19 

35.69 
0.41 
0.57 
1.75 
0.33 

ii!so 


46.75 
17.61 
16.79 

'9.4(3 
5.12 
2.56 
0.55 
0.25 

'6!92 


42.44 
25.51 
19.20 

'6!37 
0.21 
0.56 
0.49 
0.29 

io!92 


4.13 
4.19 
2.35 

MnO 
4.33 

44.79 
0.30 
0.16 
0.35 
3.04 

34.10 

2!26 


33.69 

30.30 

1.99 

14.98 
3.91 
0.26 
0.61 
0.96 
2.54 
0.00 

io.'76 


Total.. . 


100.S5 


100.50 


99.56 


101.00 


100.7S 


100.86 


100.01 


99.99 


100.00' 100.00 



In 1848 Eogers Brothers ' carried on some experiments to show 
the power of carbouate^^l water in dissolving minerals of dilferent 
kinds. The minerals were powdered and digested for 48 hours in 
carbonated water, and from 0.4 to 1 per cent of the whole mass was 
dissolved. When 40 grains of powdered hornblende were digested 
for 48 hours in carbonated water at a temperature of 60 degrees F.. 
the following percentages were dissolved: Silica. 0.08; oxide of 
iron, 0.095; lime. 0.13: and magnesia. 0.095. It is to be under- 
stood that this process will not take place so rapidly under natural 
conditions because the minerals are more massive, but at the same 
tim^ the process is going on constantly. Eichard ^liiller has shown 
that durino; seven weeks of treatment of minerals with carbonated 



WEATHERING 



23 



water that 0.533 per cent of the entire weight of oligoclase, 1.536 
per cent of hornblende, 0.307 per cent of magnetite, 2.018 per cent 
of apatite, 2.111 per cent of olivine and 1.211 per cent of serpen- 
tine were dissolved. The calcium, magnesium, and other alkalis 
were in solution in the form of carbonates. Carbonated water acts 
very readily upon limestone, and the caverns found in our large 
limestone deposits in Illinois, Indiana, Kentucky, and Virginia bear 




: Fig. 13. — Stalactites and stalagmites formed in a cavern from limestone dissolved by 

carbonated water while passing through the rocks above. Rooks, Rock-Weathering 

and Soils, Merrill. (Courtesy The Macmillan Company.) 

evidence of the great solvent power of water. It is stated that there 
are 150,000 miles of subterranean passageways in the limestone 
region of Kentucky, and practically all of this material was removed 
by carbonated water. In these caves the stalactites and stalagmites 
owe their origin to the limestone dissolved by the water before it 
enters the cavern (Fig. 13). The solution of the limestone has 
produced sinkholes on the surface that gives a peculiar topography 



24 



SOIL PHYSICS AND MANAGEMENT 



to cave regions. These sinkholes or basins vary in size from ten to 
two hundred feet or more across and from three to fifty feet in 
depth (Fig. 14). They vary in frequency as well as size. In some 
localities there are only a few small ones that are not objectionable. 




Fig. 14. — Sinkholes in a cave region — Southern Illinois. The bottoms of the sinkholes are 
still occupied by brush. (H. C. Wheeler.) 

while in other regions they are so large and frequent that the land 
is entirely worthless for cultivation. When the outlet from these to 
the cave becomes clogged, "sinkhole ponds" result (Fig, 15). In 




riu' outlets of sinkholes sometimes become clogged and "sinkhole" ponds 
result. (H. C. Wheeler.) 



WEATHERING 25 

Hardin County, Illinois, a lake varying in size from 100 to 400 
acres was produced by the stopping of the sinkhole outlets. 

The process of solution forms soil material by the removal of 
soluble substances, as in the case of limestone, leaving the impuri- 
ties, or as in sandstone, by taking out the cementing material, leav- 
ing the incoherent sand, and in the case of igneous rocks removing 
some of the potash, soda, lime, magnesia, or some other compounds, 
and leaving a residue more or less modified as soil-forming material. 

From the amount of lime carbonate carried by the Thames Eiver 
it has been estimated that the average amount of this material dis- 
solved from the limestone area drained by this stream is l-iS tons 
per 'Square mile in one year.*' It is estimated that on the average 
something like one-third as much matter is carried to the sea 
in solution as in the form of sediment, and that by this 
process alone land areas would be lowered something like one 
foot in 13,000 years.^" 

(g) Plants.- — The roots secrete acids that attack the rocks and 
aid solution. The roots of a plant growing on a polished marble 
surface removed the polish by acid from the roots showing the action 
of the acids on the rock. While this action in the case of a single 
root is very slight, yet it plays a rather important part in aiding 
decomposition because of the infiuite number of roots coming in 
contact with the soil particles and their long-continued action. 
This may be shown where the surface of stones are covered with 
lichens. Enough rock is broken down to give higher plants, such as 
ferns, a chance to grow,, and these in turn by the action of their roots 
and other agencies produce more soil nmterial that encourages still 
higher plants to grow. These plants hold the material in place and 
allow sufficient accumulation to form soils. The action of the roots 
of plants on the minerals in 'soils is very important while they are 
alive, and even when they decay they aid materially in the solution 
and liberation of plant food and decomposition of rocks. 

(h) Animals. — Many animals burrow in the soil, and their 
action on the minerals tends to aid decomposition and disintegration. 
This is especially important in the case of earthworms, ants, and 
similar animals. Many of these carry vegetable matter into the soil, 
which, by its decomposition, aids in the breaking down of minerals. 
Earthworms pass large quantities of soil through their bodies, 
the minerals of which are acted upon by the acids in the alimentary 
canal and partly decomposed. Even the larger rodents, such as 
gophers, ground squirrels, and mice exert considerable influence iu 



26 SOIL PHYSICS AND MANAGEMENT 

the formation of soils, both in tlie breaking down of minerals and m 
mixing of soil and subsoil. 

QUESTIONS 

1. Define weathering. 

2. Distinguish between the two forms. 

3. Does kaolin change into other minerals? Why? 

4. In what ways do heat and cold disintegrate rocks? 

5. Why does not a single hard freeze break all frozen rocks into fragments? 

6. Give the principal glacial areas of the present time. 

7. What is the law for the work of streams? 

8. Give some good local example of erosion. 

9. How do tiie waves do their work? 

10. Why is the wind such an effective erosive agent? 

11. Wliat is the source of each of the acids that aid in weathering? 

12. Why does the soil air contain more carbon dioxide than the atmosphere? 

13. How does oxidation hasten the breaking down of rocks? 

14. Does deoxidation aid in mineral decomposition? 

15. Bring in a sample of feldspar that shows hydration. 

16. Calculate the percentage of lime lost from each rock given in table on 

page 22. 

17. Calculate the loss of magnesia in the same way. 
IS. How are stalactites and stalagmites formed? 
19. Why are limestone soils so frequently acid? 

REFERENCES 

^American Journal of Science, volume xxii, 1832, p. 136. 

^Dutton, C. E., Tertiary History of the Grand Cafion of the Colorado. 

^Merrill, G. P., Rocks, Rock-Weathering and Soils, 1906, p. 161. 

* Hilgard, E. W., Soils. 1906, p. 19. 

^Johnson, How Crops Feed, 1910, p. 139. 

"Merrill, G. P., Rocks. Rock-Weathering and Soils, 1906, p. 160. 

^American Journal of Science, volume v, 1848. 

^Merrill, G. P., Rocks, Rock-Weathering and Soils, 1906 (Adapted), pp. 

195-202. 
" Prestwich, Quarterly Journal Geological Society, volume xxii, p. 47. 
"Reade, Liverpool Geological Society, 1876 and 1884. 



CHAPTEK III 

THE PLACING OF SOIL MATERIAL 

I. RESIDUAL, GRAVITY-LAID AND WATER-LAID DEPOSITS 

The mineral part of soils is derived from rocks through the work 
of the geological forces given. Only a small part of the disinte- 
grated and decomposed rock material produces soil where first 
formed. By far the larger portion is moved from the place of its 
origin a few feet, or it may be thousands of miles. The mate- 
rial remaining in place produces sedentary soils. 

I. SEDEISTTAET FOEMATIONS 

Sedentary Formations are those in which the greater part of 
the material was formed in place, as when Tocks weather into 
debris fitted for the formation of soils, or when large amounts of 
organic matter accumulate through the growth and jDartial decay 
of mosses, grasses, sedges, and other plants. This class of forma- 
tions is divided into residual and cunmlose soils. 

1. Residual Soils, — A residual soil is one formed in situ 
through the decomposition and disintegration of rocks and the 
action of organic agencies. It varies in composition with the rocks 
from which it is derived, and we have in general those materials (a) 
from igneous rocks, as granites, syenites, diorites, diabases and 
others; (b) from aqueous rocks, such as sandstones, limestones, 
shales; and (c) from metamorphic rocks, as gneisses, schists, mar- 
bles, and slates. By subsequent changes quite different soils result 
even from the same kind of rocks. The impression often prevails that 
most soils are residual. This, however, is not the case. Not over two 
per cent of the soils surveyed in the United States by the Bureau of 
Soils ^ are derived from igneous and metamorphic rocks, and not over 
five per cent from sedimentary rocks such as sandstones and shales. 

2. Cumulose Soils. — Cumulose soils are formed by the accumu- 
lation of organic matter in undrained areas to such an extent that 
it forms a very large portion of the soil. These are divided into 
swamps and marshes. Swamps are fresh water formations, while 
the marshes are formed in brackish or salt water areas. The organic 
matter, of these cumulose deposits is derived chiefly from mosses, 
sedges, and grasses, but almost any form of vegetation may add to 
the deposit. In north temperate and subarctic regions sphagnum 

27 



28 



SOIL PHYSICS AND MANAGEMENT 



moss gives rise to immense deposits of peat, in some cases probably 
hundreds of feet in thickness. Grasses usually grow with the 
mosses and add to the accumulation. In more southern regions, 
grasses, cattails and sedges form a large part of the deposit, while 
in subtropical regions the palmetto and saw grass constitute the 
chief plants from which the organic matter is derived. 

Swamps may be divided into river swamps, peat bogs, lake 
swamps, quaking bogs, climbing bogs, wet woods and ablation 
swamps. These terms are almost self-explanatory. River swamps 
may occur in the flood plain where ox-bow lakes, representing 




Fig. 16. — Ox-bow lakes formed by shifting of channel, A, B and C. Sedimentation on 
inner side of curve. (Shaler,) 

former channels, have been transformed into swamps by filling with 
both organic matter and sediment (Fig. 16). In wide flood plains 
low swampy land may lie back toward the bluffs away from the 
river. Delta lands are usually swampy. 

Peat deposits may be formed ( 1 ) in low places where the water 
is shallow but the supply constant (Figs. 17 and 18). This type 
is found in sand dune or gravelly areas where the water seeps out 
at the base of sand hills or gravel terraces. Peat formed in this 
way is rarely of any great depth. Peat bogs may also be formed 
(2) as shown in figure 19. The sphagnum moss begins to grow at 
the margins of the lake and extends out over the water, forming a 
quaking hog, and up the bank, as a climhing hog. The growth over 
the water is quite rapid and the small pond or lake may become 



RESIDUAL, GRAVITY-LAID, WATER-LAID DEPOSITS 29 

covered with a floating mass of vegetation which soon becomes suf- 
iiciently solid to form a support for other plants such as rushes, 
grasses, and sedges. The growth of these soon so strengthen this 
floating mass that still other species of swamp vegetation, including 




I*M 'vMIl*''"'" 




Fig. 17. — Typical eastern swamp land. The grass will be preserved from decay in 
the water. Leaves from the forest will add to accumulation. A soil rich in organic matter 
will result. 




Fig. 18. — Florida everglades. 



some shrubs, gain a foothold. Forest trees may ultimately cover 
it. While the process above described is taking place partly decayed 
vegetation is dropping to the bottom of the lake from the under 
side of the floating mass, and this accumulation may go on till the 




Fig. 19. — Section showing one step in the filling of the lake with peat; cc, moss growing 
on surface of lake; dd, partly decayed peat that has fallen from floating mass; ee, cUmbing 
bog. (Shaler.) 

pond or lake becomes completely filled. Accumulations of peat also 
occur around springs, giving rise to quaking bogs (Fig. 20). In 
poorly drained areas the moss may grow on the surface of the soil 
in sufficient amounts to form peat. Oftener, however, it forms only 
a soil rich in organic matter. 



30 



SOIL PHYSICS AND MANAGEMENT 



A wet woods swamp is where a forest area with a slope of less 
than five degrees has been transformed into a swamp through the 
accumulation of vegetable material and the consequent increase of 
moisture. The original forest may be entirely destroyed and re- 
placed by plants adapted to swamp conditions. 

An ablation sicamp is produced by the solution and carrjdng 
away of certain more soluble strata, such as gypsum, salt or even 
limestone, between less soluble strata, thus causing a lowering of 
the surface and bringing about swamp conditions. 

II. TRAXSPOETED FORIMATIOXS 

Various agencies are engaged in the movement of soil material, 
namely : gravity, water, ice, and wind, and the deposits formed by 




Fig. 20. — Hummocks 6 to 12 inches high, found in swampy places produced by trampling of 
stock. Commonly called "bogs." (R. W. Dickenson.; 

these are known as colluvial, sedimental, glacial, and eolial. During 
the transportation of these materials many particles are reduced 
in size and other changes brought about. Over ninety per cent of 
the soils surveyed by the Bureau of Soils ^ in the United States are 
formed from transported material. 

1'. Colluvial or Gravity-laid Soils. — Gravity might be said to 
be the active agent in the formation of all of the above, but gravity, 
unaided, is very limited in its work, being confined to areas of 
vertical cliffs or very steep slopes. The material transported by 
gravity and deposited at the base of cliffs consists of a heterogeneous 
mixture of detritus that has been loosened by the processes of 
weathering and carried downward by gravity. This accumulation 
is commonly designated as talus or cliff debris (Figs. 21 and 22). 



RESIDUAL, GRAVITY-LAID, WATER-LAID DEPOSITS 31 




td£j^I'ii^r°''''^'^^^^^ 



32 



SOIL PHYSICS AND MANAGEMENT 



It shows very little or no assorting action, althongh in some cases 
the finer material may be washed out by water and deposited at the 
base, thus leaving the coarser material higher up on the slope, wliile 




Fig 22. — Rock disintegration and formation of talus slope. More advanced stage. Mount 
Sneffels, Colo. (.Merrill.) 




(From Elements of Geology. Copyright iqii, by Eliot Blackwelder and Harlan H. Barrows. 
American Book Company, Publishers) 

Fiffl. 23. — The side of a ra^nne near Crawfordsville, Indiana. The more rapid creep of 
surface material has caused the trees to lean down hill. 

in other cases the coarser material may roll down the slope to a 
greater distance, leaving the finer at the top. This process of weath- 
ering and downward movement of material will finally transform 
the vertical- cliif into a steep slope which will represent the angle 



RESIDUAL, GRAVITY-LAID, WATER-LAID DEPOSITS 33 

of rest of the detritus. The downward movement does not stop here, 
for there is a certain amount of " creep ^' due to freezing and thaw- 
ing, and the action of water aided by gravity (Fig. 23) that ulti- 
mately reduces the slope so that it may be cultivated. These talus 
slopes are small in extent and are of very little agricultural value 
because of their stony character. 

2. Sedimental or Water-laid Soils.— The material forming 
these deposits has been carried in suspension or rolled along the 
beds of streams for a greater or less distance from their place of 
origin. When a body is immersed in vfater, it loses weight equal 
to the weight of the water displaced by it. This buoyant effect 
enables fine, particles to remain in suspension for a long time and 
renders coarser material more easily moved than when in the 
atmosphere. The total amount of material carried by running 
water varies as the fifth ^ power of its velocity while the size of 
particles carried varies as the sixth power, so that doubling the 
velocit}^ increases the amount of material thirty-two times and the 
size of material carried sixty-four times. If the velocity were 
trebled the amount is increased two hundred and forty-three and 
the size is increased seven hundred and twenty-nine times. Then 
if a given current carries particles .1 mm. in diameter doubling 
its velocity enables it to carry material 6.4 mm. in diameter, or 
trebling the velocity enables it to carry particles 72.9 mm. in 
diameter. The following table shows- the character of material that 
may be carried or swept along by the current. 

The Material Carried hy Water of Varied Velocity^ 

Inches per Miles per 
second hour 

3 0.170 — will just move fine clay. 

6 0.240 —will lift fine sand. 

8 0.4545 — will lift sand as coarse as linseed. 

12' 0.6819 — will sweep along fine gravel. 

24 1.3638 — will roll rounded pebbles 1 • inch in diameter. 

36 2.045 — will sweep along slippery, angular stones the 

size of an egg. 

Another factor in the transportation of soil material is given 
by King.* When a particle is immersed,'it attracts a film of water, 
which becomes an essential part: of the particle, moving with it 
wherever it goes.' The specific gravity of soil particles is approxi- 
mately 2.65. The immersed solid-liquid body has such low specific 
gravity that very little force is required "to keep it in suspension 
and so it becomes possible for a particle to be carried hundreds of 
miles. This adherent film averages about .05 mm. in thickness. By 
computation we find that a clay particle .001 mm. in diameter with 
3 



34 



SOIL PHYSICS AND MANAGEMENT 




RESIDUAL, GRA.VITY-LAID, WATER-LAID DEPOSITS 35 



a film .01 mm. thick lias a specific gravity of 1.0003. This is so near 
the specific gravity of water that the particle will remain in suspen- 
sion indefinitely. Professor King estimates that a force of only 4.4 
pomids is necessary to keep the 11 tons of sediment in suspension 
that is delivered at the mouth of the Mississippi River each second. 
The increase of the elfective diameter of the particle augments the 
effective cross-section 441-fokl, and so only a very small vertical 
motion would be required to maintain suspension. The effective 
volume would be increased 9,261-fold by the adhering film. When 
a particle of dust is suspended in the atmosphere it attracts a film 
of air which moves with it in the same way as the film of water and 
lessens its specific gravity, thus enabling it to be held in suspension 
with a much smaller force than would otherwise be necessary. The 
specific gra-vdty of a clay particle .001 mm. in diameter, with an 
adherent film of air, is 1.2336. For computing the specific gravity 
of a 23article immersed in water the following formula may be used : 



Sp. Gr.: 



Trd^X pp. gr, 
6 



/ ttD^ 7rd3 \ 
^ \ 6 6 / _ 



rD3 
6 



6 
= volume cf a sphere. 



d^X sp.gr. -I- (D^-d^) 
D3 



d = diameter of particle or solid nucleus 

sp. gr. = specific gravity of the nucleus 

D = diameter of solid-fluid system 

Sp. Gr. = specific gravity of the solid-fluid system 

The amount of material carried by the Mississippi River and 
deposited in the Gulf of Mexico annually is equivalent to the re- 
moval in 6,000 years of a layer one foot thick over the entire drain- 
age area. 

Amoimt of Sediment Carried in Suspension Annually ^ 



River 


Drainage 
areas in 
sq. mi. 


Mean 

annual 

discharge 

in cu. ft. 

per second 


Total 

tons 

annually 


Ratio of 
sediment 
to water 
by weight 


Height 

in ft. of 

column of 

sediment, 

base 
1 sq. mi. 


Thickness 
of sedi- 
ment in 
in. if spread 
over drain- 
age area 


Potomac . . . 
Mississippi . 
Rio Grande. 
Uruguay. . . 

Rhone 

Po 


11,043 

1,244,000 

30,00C 

150,000 

34,800 

27,100 

320,300 

1,100,000 

125,000 

334,693 


20,160 5,557,250 

610,000 ^06,250,000 

1,700 3,830,000 

150,000 1 14,782.f00 

65,850 i 36,000,000 

62,200 67 000 000 


1 


3,575 
1,500 

291 

10,000 

1,775 

900 
2,880 
2,050 
1,610 

: 2,731 


4.0 

241.4 

2.8 

10.6 

31.1 

59.0 

93.2 

38.8 

209.0 

76.65 


.00433 
.00223 
.00116 
.00085 
.01075 
.01139 


Danube. . . . 

Nile 

Irrawaddy.. 

Mean 


31.5,200 
113,000 
475,000 

201,468 


108,000.000 

54,000,000 

291,430,000 

109 64P.P72 


.00354 . 

.00042 

.02005 

.00614 



36 



SOIL PHYSICS AND MANAGEMENT 



Classes of Sedimental Soils. — There are three cLisses of sedi- 
mental soils, marine or sea-laid, lacustrine or lake-laid, and alluvial 
or stream-laid. 




Fig. 25. — Map showinj: the early stages in the formation of coast marshes. The numbers 
indicate the depth of water in fathoms. CC. and G. Survey.) 

(a) The marine or sea-laid deposits are formed along sea coasts 
(Fig. 25) and include bars, spits, hooks, and marshes. Bars fre- 
quently produce lagoons that ultimately become marshes. Marine 

M0vTid^ 

Sea, _ -, , 

Low Tide 

•—- , d ■ 




FtG. 26. — Section of marine marsh; 6, grassi marsh; c, mud bank, or mud flats; d, eel-grass. 

CShaler.) 



RESIDUAL, GRAVITY-LAID, WATER-LAID DEPOSITS 37 

and salt marshes are divided into those above mean tide, as the 
grass marshes and mangrove marshes, and those below mean tide, 
mud banks and eel-grass areas (Fig. 26). The mangrove marshes 
occur along the Florida coast and have played a very important 
part in adding to the land area (Fig. 27). The other form of 
marshes occur in more northern regions, the grass marshes being 




Fig. 27. — Mangrove marsh, Biscayne, Florida. This mangrove advances into the 
water by throwing out new roots. (From Elements of Geology. Copyright 1911, by 
Eliot Blackwelder & Harlan H. Barrows. American Book Company, Publishers.) 

sufficiently high so that they are covered only during the highest 
tides. The eel-grass banks are always covered, while the mud bank 
is intermediate between these. Holland is an illustration of what 
the marsh lands may become when drained and protected by dikes, 
(b) Lacustrine. — Lacustrine or lake-laid dejDosits consist of 




Fig. 28. — Level floor of Lake Chicago, with the shore-line in the distance. (R. W. Dickenson.) 

(1) terraces and beaches representing old water levels and shores 
and (2) the beds of extinct lakes. During glacial times, many 
lakes were formed by the obstruction of drainage and many more 



38 



SOIL PHYSICS AND MANAGEMENT 



were filled to a greater or less height with gTavel and sand. Lake 
Agassiz^ covering a large area in Minnesota, Xorth Dakota, and 
Canada, represents the former, while Lake Chicago (Fig. 28), an 
extension of Lake Michigan to the south, and Maumee Lake, an 
enlargement of Lake Erie, are examples of the latter (Fig. 41). 




Fic. 29. — Terraces of Frazier River at Lilloet, B. C. Six in number. (Chamberlain and 
Salisbury, Courtesy Henry Holt & Co.) 

All of the Great Lakes were much more extensive then than now 
and subsequent drainage lowered the water and exposed parts of the 
old bed which now constitute lacustrine deposits. These give us 
some of our best soils. Loess and adobe may be formed, in part 
at least, in lakes. 

(c) Alluvial. — The alluvial, or stream-laid deposits, include, 
first, terraces, commnnlv eallerl second bottom or bench lands, that 




Fig. 30.— Tenuc 



aldiit: Crffk, HL-ar Rorkford, Illinois, shownng stratification. 
Stewart.) 



(H. W. 



RESIDUAL, GRAVITY-LAID, WATER-LAID DEPOSITS 39 

represent the former liooil plains of streams which now flow at a 
lower level; second, first bottom lands, or present flood plains; third, 
deltas ; and fourth, alluvial cones and fans. 

Terraces originate in three ways: (1) those formed by depo- 
sition of material from overloaded streams givmg rise to sand, 
gravel, or silt terraces (Fig. 29). These occur prmcipally along 
tlie streams that carrier! the drainage from the meltmg glaciers. 

When the current decreased, the 
load was dropped and the valleys 
were filled to a greater or less 
height with gravel and sand. In 
some cases the valleys were filled 
almost to a level with the upland 
(Figs. 30 and 31). Farther 
down the stream the terrace be- 
came lower and the finer material 
was deposited. When the glacier 
retreated, the stream, having no 
load to carry, would begin to cut 
down through the gravel and 
soon this formation would be 
much above the stream and con- 
stitute a terrace, second bottom, 
or bench land. The same action 
might take place down the stream 
where the finer material was 
deposited. (2) Those formed 
through elevation of land and 
consequent rejuvenation of the 
stream, thus causing it to cut 

Fig. 31.— Closer view section of gravel terrace doWll thrOUgll and abandon the 
of Fig. 30. (H. W. Stewart.) , ^ _ ^ , . , „ ^ 

old flood plain and form a new 
one. (3) Those formed by pondo'nc/ of fnhutary streams due to the 
building up of the flood plain of the main stream more rapidly than 
that of the tributaries. In this way the lower part of the tributary 
valley is formed into a lake which would receive a deposit of fine 
material from the tributary but coarse from the inrushing waters 
from the main stream during floods. A reduction of the water 
supply and the amount of sediment carried by the main stream 
will enable the tributary to cut dnvra into the flood plain, drain the 
lake, and form a new valley in the fill. Good examples of this are 




4:0 SOIL PHYSICS AND MANAGEMENT 

soeu aloiiir the tributaries of the ^Mississippi ami Wabash Rivers. 
The very heavy soils along tliese have been lormeil in this way. 

QUESTIONS 
1. What are sexlentary formations? 
•J. Distinguisli betwoon resiihial aiul cuuuilose soils, 
o. IJive history of an ox-Ik>\v hike: its formation aiul tilling. 

4. Give four ways in whioh lakes nuiy beeome extinct. 

5. What conditions give rise to peat? 
0. HoNV is peat formed? 

7. What is a elimbing bog and how formed? 

S. How may a wet woods become a swamp? 

5>. Draw a diagram showing how ablation swamps may be formed. 

10. How are coUuvial soils formed? 

11. What is meant by the "creep" of material on hillsides? 

12. What are the laws for the can\ving power of running water. 

13. t>i\e an example of this power. 

14. What is the specitic gravity of a soil particle .01 mm. in diameter and 

its inclosing film of water .0"> mm. thick? 
lii. How long would he reipiired for the Potomac River to remove \2 inches 

of material from its drainage basin at the rate given in table p. ."lo? 
1(). What are t!>e divisions made of marshes? 
17. What are the forms of lacustrine deposits? 

15. How are terraces formed ? 

REFERENCES 

Mlarlmt. C. F.. Bennett. H. H., Lapham. J. E.. and l.apb.am. M. 11., ruilletin 

0(i. Bureau of Soils. I". S. D. A.. l!)13. p. 10. 
'Deacon, G. P., Inst. Civil Kngineering rroceedings. volume IIS. ISJU, 

p. 03-5H5. 
^tieikie. Textbook of Geology, .^rd edition. 

* King, F. H.. Suspension of Solids in Fluids and the Nature of Colloids 

and Solutions. Transactions Wisconsin Acad. Sci.. Arts and Letters, 
volume lli, part 1. lOOS. 

* Babb. Science, volume 21. ISOo. p. ;>4o. 

General References. — ^IcGee. W. J.. Bulletin 71. Bureau of Soils. 
U.S.n.A.. Ptll. Soil Erosion. Davis. K. O. E.. Bulletin ISO. C.S.D.A.. 1!>15. 
Soil Erosion in tlio South. Salisbury. R. D.. Agencies which Transport 
Material on the Earth's Surface, Journal of Geology* volume iii, p. 170. 



CHAPTETI IV 

THE PLx^CING OF SOIL MATERIAL (Continued) 
II. GLACIAL OR ICE-LAID DEPOSITS 

Tile glaciers and ice «lieets of i'onner times covered extensive 
areas with deposits of material that may be divided into morainal, 
iiitermorainal, drmiiliiis, kames, and eskers. During the glacial 
])c'riod, practically all of North America north of the Ohio and 
Missouri Elvers, amounting to 4,000,000 square miles, Avas covered 
with an ice sheet (Fig. 32) that had gradually pushed southward 




Fig. 32. — Front of Chenega Glacier compared with Washington Monument, 550 feet high. 

(Lawrence Martin.) 




Fig. 33.— Very stony and gravelly phase of glacial drift near Whitewater, Wisconsin. 

(King.) 

41 



42 



SOIL PHYSICS AND MANAGEMENT 



from three centers of accumulation in Canada. The northwestern 
half of Europe was covered at the same time. Vast quantities of 
material of all sizes and all kinds of rocks were transported and 
deposited when the ice melted^ leaving a mantle of boulder clay, 
drift, or till, varying from a few inches to several hundred feet in 
thickness. The average depth of the deposit for Illinois, according 
to Leverett,^ is about 115 feet. These glacial deposits constitute the 
material from which the soils were formed over a large area east and 
north of Illinois, but in the middle west a deposit of loess has 
buried- the drift, producing soils of an entirely different character 
(Fig. 33). In glaciated Europe the same conditions exist in regard 
to soils. 




Fig. 34. — Limestone boulder showing glacial scratches. Urbana, 111. 

The drift left by glaciers is only one of the important things 
accomplished by them. The enormous pressure of the ice, 40 pounds 
per square inch for each hundred feet in thickness, enabled it to 
wear down hills and fill valleys, especially if they extended nearly 
at right angles to the direction of the movement. Otherwise it 
might deepen and broaden them, but on the whole its effect has been 
to leave the country more nearly level than before. Many regions 
have been transformed from hilly areas of low agricultural value 
to undulating or rolling lands well adapted to agriculture. The ice 
in its movement southward picked up large quantities of detritus 
of all kinds and sizes and ground it into fine material fitted to form 
soils. Much of this material was carried from 400 to 1,000 miles 
or more and during its transportation boulders (Fig. 34) and gravel 
would rub and grind against each other and against the rock' sur- 



GLACIAL OR ICE-LAID DEPOSITS 



43 



faces over which they moved (Fig. 35), producing immense quan- 
tities of rock flour. The whole glacier was an immense mill that 
was slowly grinding rocks into powder. This rock flour was lib- 




FiG. 35. — Glacial grooves or striae ou lock Miilaic. i\oilhern Ohio. (From Elements of 
Geology, Copyright 1911, by Eliot Blackwelder & Harlan H. Barrows. American Book Co.) 




Fig. 30. — Typical topography of terminal moraine near Ocomowoc, Wisconsin. Wisconsin 
Geol. Survey. (Fenneman.) 

erated by the melting ice and was distributed over the land by water 
and wind, forming the very best of soil material. In some in- 
stances it was carried much farther than the limit of the ice sheet 
and distributed as immense aprons beyond the ice front. 



44 



SOIL PHYSICS AND MANAGEMENT 




Fig. 37. — Drumlins — remnants of former terminal moraines. (U. S. Geol. Survey.) 




Fig. 3S. — Drumlin — transverse view. By Alden. (U. S. Geological Survey.) 




Fig. 39. — Adeline esker, Ogle County, Illinois. This esker is over nine miles in length. 

(,R. W. Dickenson.) 



GLACL4L OR ICE-LAID DEPOSITS 



45 



The material carried and pushed along by the ice is usually very 
irregularly distributed, giving the glaciated areas an undulating 
to rolling topography. The ridge formed at the terminus of the 
glacier is the terminal moraine (Fig. 36). It usually presents 
a steep outward slope with a very gradual inward slope. The 
surface of the moraine is rolling, billowy, or has "rounded knob and 
basin" topography. The height of moraines may vary from a few 
feet to several hundred, while the width may be from a half mile 
to ten miles or more. Recessions and advances of the glacier may 
Ijuild up new moraines or override old ones, tearing them down 
completely or transforming the material into lenticular hills, called 
drum.lins (Figs. 37 and 38), whose longer axis is in the direction 
of movement of the latest ice sheet. 

Super- and subglacial streams formed hills of gravel and sand 
called lames, or ridges of the same material called eskers (Figs. 39 
and 10). 




Fig. 40. — The material composing Adeline esker consists of coarse sand and gravel. 
The ledge is conglomerate formed by cementing the sand and gravel with carbonate of lime. 
(R. W. Dickenson.) 

The Glacial Period. — The three centers of accumulation in 
North America during the glacial period were the Labradorean in 
Labrador, the Keewatin immediately west of Hudson Bay, and the 
Cordilleran in the Rocky Mountains of Canada. These centers cov- 
ered large areas (Fig. 42), and ice movement started from these in 
practically all directions, but probably not from all centers at the 
same time, or at least not to the same extent. Smaller centers of ac- 



46 



SOIL PHYSICS AND MANAGEMENT 



cumulation existed in the Kooky and Sierra Nevada Mountains and 
on the Island of ISIewfoundland. In Europe (Fig. 43) the Scandina- 
vian was the i^rincipal and the Ural, a secondary center. The glaciers 
of the Alps and Caucasus were much more extensive than at present, 
(a) The Jerseyan or Nebraskan Glaciation and Af Ionian 
Interglacial Stage. — The first glacial advance probably came from 
the Keewatin center and is called the Jerseyan or the Nebraskan, 
because small areas of surface deposits made by this glacier are 
found in those states. All other deposits of this advance have been 
buried by subsequent ice sheets and it is difficult to make a careful 
study of them because of superposed material. There is no evidence 
that the area between New Jersey and Nebraska was covered by 




Fig. 41. — Map showing extent and southern limit of glaciation in North America. 
Also Lakes Agassiz, Lahonton and Bonne\'ilIe. (Compiled from several sources.) 



this ice sheet. This glacier receded and the drift deposited by it 
became eroded, weathered and the surface was changed into soil. 
Even peat beds were formed in undrained areas. Tliis inter- 
glacial stage is knoT\Ti as the Aftonian. 

(b) The Kansan Glaciation and Yarmouth Interglacial 
Stage. — The second glacial advance Avas from the Keewatin center 
also, and extended into Iowa, Illinois, Nebraska, and Kansas, and 
derived its name from the exposure of drift in the latter state. 
After the ice receded soil was formed from the siirface of the drift 



GLACIAL OR ICE-LAID DEPOSITS 



47 



and organic matter accumulated as peat in some swampy areas. 
This stage is known as the Yarmouth. 

(c) The Illinoisan Glaciation and Sangamon Interglacial 
Stage. — The third glacial advance was from the La1:)radorea.n 




Fig. 42. — Map showing the three centers of ice accumulation in North America. 
berlain and Salisbury. Courtesy Henry Holt & Co.) 



(Cham- 



center and was the most extensive in the middle west during the 
entire period of glaciation. The greatest area of surface deposits is 
in Illinois, hence the name. It is exposed in Oliio, and Indiana, also. 
This glaciation was followed by a long interglacial stage during 
which weathering and soil formation occurred. It is known as 



48 



SOIL PHYSICS AND xMAXAGExMENT 



the Sangamon stage (Fig. 4-1:). Peat deposits have been found as 
much as '^v' feet in thickness that Avere formed during this period, 
(d) lowan Glaciation. Loess Deposits and Peorian Inter- 
glacial Stage. — The Sangamon interghieial stage was followed 
by the lowan advance from the Keewatin center and covered a con- 
siderable part of Minnesota. Wisconsin, northeastern Iowa and the 
northern part of Illinois. The conditions at the time of the melting 
of this glacier gave rise to extensive loess deposits. During sum- 




Fio. 43. — Map showing extent of ice-sheet, Europe. (Reproduced from Dana's Manual of 
CJeolog}-, by special ammgement with American Book Company.) 

nier the melting was very rapid so that the Hood plains of streams 
draining from the glacier received deposits of rock Hour during 
these periods of overflow. During times of little melting the 
streams contracted to their ordinary channels, leaving the material 
exposed on their flood pdains. This was picked up by the wind and 
distributed over the upland where it occurs as a deposit from 3 to 
loO feet in thickness over part of the states bordering the ^fississippi 
and Missouri Eivers. The loess buried the Sang-amon soil. 

The Peorian interglacial stage followed the lowan glaciation. 



GLACIAL OR ICE-LAID DEPOSITS 



49 




benefth'-md"H,^ wl? l ^''°'^' k^ ^^'^ black Sangaiaun soil with the Illinois glacial drift 
iCs' Tf. Lrveieu!V;irGfors;.;ve?.)'^' ^''''''' '°'' ""^ the surface. Kr.ox County. 




Fig 45,— a section sh„^Mnn (a) Rl„.,n,inKton Kra^ el (b) Sh, Un Mile till sheLt lul a an 
loess; (d) Sangamon soil, (e) Silt below ceat (Dr Samuel Cah in, U. SGeol Survey.) 



50 SOIL PHYSICS AND MANAGEMENT 

during which the surface loess was changed inco soil which was 
later buried in part b}'' subsequent glaciers. The soils and peat beds 
of the Peorian stage contain remains of cedar trees which grew In 
the extensive swamps that existed at that time. 

(e) Early Wisconsin Glaciation, Loess and Interglacial 
Stage. — The Peorian stage was ended by another ice advance known 
as the Early Wisconsin (Fig. 45), which came from the Labra- 
dorean center of accui^iulation and formed a very extensive advance 
reaching into Iowa, Illinois, Indiana, Ohio, Pennsylvania and cov- 
ering practically all of A^ew York and the Xew England states. 
This glacier built up a system of moraines in the middle west that 
is one of the most characteristic features. The terminal moraine 
of the greatest advance is usually a distinct ridge. In Illinois and 
Indiana it is known as the Shelbyville moraine. This glacier made 
several advances and recessions, building up a moraine T^dth each 
advance, giving a series somewhat concentric with Lake Michigan 
and other Great Lakes. A deposit of loess covers this drift in 
Illinois and parts of Indiana to a depth of from three to six feet. 
This glaciation was followed by a comparatively short unnamed 
interglacial stage. 

(f) Late Wisconsin Glaciation. — This stage was terminated 
by an ice advance, the late Wisconsin, from all centers of accumula- 
tion and in addition from many local centers. . It was one of the 
m,ost extensive and uniform ice sheets during the entire glacial 
period. The ice front did not extend southward a^ far as some 
other advances except in Xew England, but there was probably a 
solid ice front from the Atlantic to the Pacific. The erosive and 
transporting power of the ice seemed to have been greatest at this 
time, as is shown by the very high and characteristic moraines 
formed near some of the Great Lakes. 

Incidental Features, — Certain incidental features were de- 
veloped in connection with the glaciers that served to modify the 
soils in many regions. The drainage from the melting ice during 
part of the time was entirely to the south. The streams were flooded 
and overloaded- with sediment, the deposition of which Iniilt up ter- 
races of gravel, sand, silt, and even clay. When the glacier had re- 
ceded so that the region in northern United States was partly cov- 
ered, the outlet of the lakes, which is naturally to the north and 
northeast, was obstructed so that they overflowed the margin of the 
basins and drained into the Mississippi Eiver. Lake Agassiz, the 
enlarged Lake Winnipeg, is responsible for the soils of the Red River 



GLACIAL OR ICE-LAID DEPOSITS 



51 



valley. (Fig. 41). Lake Chicago, the extension of Lake Michigan, 
I^iake Maumee, an extension of Lake Erie, and other lakes at Green 
and Saginaw Bays produced lake-laid soils and formed characteristic 
beaches. 

The material deposited by the glaciers is of every grade from 
the finest clay to boulders Aveighing many tons (Fig. 46). Its value 




Fig. 46. — Granite boulder wei^liing about 3U tons, at depot of Northwestern R. R., 
Waukegan, 111. 




Fia. 47. — Heap of boulders collected from a moraine in northern Illinois, 
(R. W. Dickenson ) 



52 SOIL PHYSICS AND MANAGEMENT 

for forming soils depends upon its fineness and the rocks from 
which it was derived. Many areas kno\m as boukler belts contain 
so many boulders that it is impossible to cultivate the soil, while 
iu others they were not so abundant but that it is practicable to re- 
move them. These boulders are sometimes used for making fences, 
or piled up on waste land (Fig. 47). 

In many cases where the glacier passed over rather soft rocks, 
such as sandstones or shales, large amounts of this were picked up 
and pushed along and sometimes formed a very large part of the 
deposit. The soil formed from it is very inferior. Where the crys- 
talline rocks, such as granites and syenites, are mixed with lime- 
stones a very fertile soil results. 

Most of the boulder clay is sufficiently fine for good soils, al- 
though nearly the entire glaciated area cont^ains some boulders. 
In the middle west the drift is covered with a layer of fine wind-laid 
material. 

QUESTIONS 

1. What was the extent of tlTe ice slieet ihiring the ghieial period? 

2. To wliat extent was material deposited? 

3. What pressure did the ice exert? • 

4. How are terminal moraines formed? 

5. Distinguish between kames, eskers, and drumlins. 

6. Name and locate the centers of accumulation in Xorth America and 

Europe. 

7. Tell about the Jerseyan or Xebraskan glaciation. 

8. Give the facts in regard to the Kansan advance. 

9. Tell about the lllinoisan glaciation. 

10. What was characteristic of the lowan? 

11. \\hat was the extent of the Early Wisconsin advance? 

12. What was the extent of the area covered by the Late Wisconsin? 

13. What ettect did this have on drainage? 

14. Give some illustrations. 

15. What are boulder belts? 

16. What was the general elTeet of glaciers on soils? On topography? 

17. What is boulder clay? 

REFERENCES 

^Leverett. F., Illinois Glacial Lobe. ^lonograph 38, U. S. Geol. Survey, 
1899, p. 549. 

General References. — Leverett and Tavlor. Monograph 5.3. U. S. Geol. 
Siirvey. The Pleistocene of Indiana and ^Michigan and the History of the 
GreatLakes. 1915, op. Cit. Complete Bibliosraphy. pp. 33-54. Chamberlain 
and Salisbury, Geology, volume iii. Earth History, The Cause of the Glacial 
Period, pp. 42 4-44(i. " Wright. G. F.. The Ice Age of Xorth America and Its 
Bearing on the Antiquity of :Man, New York, 4th ed., 1896, pp. vii-xxv, 
315-358. 



CHAPTEE V 

THE PLACING OF SOIL MATERIAL (Continued) 
III. EOLIAL OR WIND-LAID DEPOSITS 

The statement has been made that every square mile on the 
earth's surface has received particles from every other square mile. 
Whether this is absolutely true or not, it shows that- a very wide 
distribution of material has been going on, and this distribution 
has been brought about by the agency of wind. No place on the 
earth's surface is free from dust. Even the snow on the great 
continental ice slieet of Greenland contains a perceptible amount. 
Dust storms all over the world are carrying fine material into the 
upper atmosjDliere, where it is transported for thousands of miles, 
falling on all parts of the earth. Dust falls have occurred in which 
a measurable amount has fallen in a few hours. In Indiana in 1895 
a snow fall was colored brown by the large amount of dust it con- 
tained. One sample, collected just after the storm, contained .37 
per cent of dust by weight. The same year a sample of snow 
collected in London contained 10.65 grains of solid material per 
gallon of water from the melted snow. Darwin observed that the 
water in the Atlantic 300 miles from the coast of northern iVfrica 
was distinctly colored by the dust, and that dust was falling in the 
ocean in perceptible quantities 1,600 miles from the- Desert of 
Sahara. The sirocco winds of the Sahara sometimes carry dust in 
perceptible quantities as far north as Scotland. Professor J. A. 
Udden ^ estimated that during an ordinary breeze a cubic mile of 
air will contain 225 tons of dust, while in a heavy storm it will 
contain 126,000 tons (Fig. 48). The dust picked up by winds 
together with that thrown into the atmosphere by volcanoes has 
played an important part in the formation of soils. 

Classes of Wind-laid Material. — The wind-laid deposits are 
dunes, loess in part, adobe in part and volcanic dust. 

1. Dunes. — Sand is the common constituent forming dunes, 
but other materials sometimes compose them. Clay and silt dunes 
are not unusual. Coffey " found clay dunes in southern Texas, 
while silt dunes are frequently met with in areas of deep loess. 
Many of these are found on the eastern borders of the Mississippi 

53 



54 SOIL PHYSICS AND MANAGEMENT 

and Illinois Elvers, notably in Carrol, Whiteside, Eock Island and 
St. Clair Counties in Illinois. The conditions necessary for the 
formation of sand dunes are a supply of sand and a somewhat higli 
and constant wind. Sea and lake shores furnish excellent conditions 
for the formation of sand dunes. The waves throw the sand upon 
the beach and the strong- winds which so often prevail there carry 
it landward. Shaler estimates that ninety per cent of the coast line 
of the world is fringed with sand. The total dune area of Europe 
is -1.562,000 acres, while the sand wastes add about 9,000,000 acres 
more. 




Fig. 4S.— a dust storm in Kansas, May 26, 1012. (Jardine, Jour. Am. Soc. Agronomy, 

Vol. o. No. 4.) 

Sand is not raised far above the surface as in the case of dust, 
and a shrul\ a tuft of grass or a fence may give lodgment to the 
sand and origin to a dune. After accumulations have once begun by 
means of an obstruction, the dune itself will furnish the necessary 
conditions for growth. In shape, dunes may be either in the form 
of hillocks, crescents, or ridges, transverse or parallel to the pre- 
vailing- winds. The shape of the individual dune is a steep leeward 
and a gradual windward slope, especially where the prevailing wind 
is constantly from the same direction. 

Sand dunes are of two classes, migratory or wandering (Fig. 
49), and permanent or fixed. With a constant wind, dunes migrate 
or advance a few feet each year, burying objects in their paths. 



EOLIAL OR WIND-LAID DEPOSITS 



55 



Even villages and forests cannot Avithstand the advance of sand 
dunes. The usual height is from ten to thirty feet^ but some have 
been found 300 feet high. Through some temporary change in 
climate, as increased rainfall or diminished wind velocity, vegeta- 
tion may start on the sand and gain such a foothold that the dune 
becomes fixed or permanent. This fixed feature is sometimes 






Fig. 49. — Sand dune advancing over forest, Beaufort Harbor, N. C. (U. S. Geol, Survey.) 





Fig. 50, — A resurrected forest, Dune Park, Indiana. (Chamberlain and Salisbury, Cour- 
tesy Henry Holt & Cq.) 



56 



SOIL PHYSICS AND MANAGEMENT 



brought about by plantings on the windward side. In Denmark, 
Prussia, Scotland, Massachusetts, and Xorth Carolina, beach or 
marram grass (Fig. 52) whose roots extend to a great depth 




Fig 51 — Wind ripples on sand dune. (Cross, Chamberlain and Salisbury, 
Henry Holt & Co.) 




Fig. 52.— Transplanting beach or marram grass. (Bureau of Plant Industry.) 



EOLIAL OR WIND-LAID DEPOSITS 



57 





Fig. 53.— The gra.ss in the foreground holds the sand which drifts from the "waste 
beyond the fence. (U. S. Dept. of Agriculture-^ 




FiQ. 54.-Sand is being held by> vegetation In this way wandering dunes may be changed 
to permanent ones. (U. S. Dept. of Agriculture. "> ciiaiigeq 



58 SOIL PHYSICS AND MANAGEMENT 

has been used quite extensively to hold the sand. This grows 
luxuriantly as long as the sand is drifting, but dies and is re- 
placed by other forms of vegetation as soon as movement ceases. 
After fixation is accomplished certain varieties of trees may be 




,»>. 



^^ 






-m 






Fig. 55. — Fences being used to check the movement of sand. (U. S. Dept. of Agriculture.) 

planted, transforming these dunes into valuable forest lands. 
Permanent or fixed dunes may be changed to migratory ones by 
injudicious management, such as very close grazing, tillage 
or anj-thing that destroys or removes the protecting vegetation. 
This has occurred in some western states where close grazing by 
sheep has destroyed the vegetation so that sand movement has 
■begun. Michigan, Illinois, Wisconsin and Indiana have consid- 
erable areas of sand dunes. A large part of these areas is covered 
with a scrubby growth of black oak and other trees, which furnish 
complete protection. When this gi'owth is removed, however, it 
is very difiicidt to hold the sand and it is the part of wisdom to 
leave even the" poor gro\\d;h of forest for purposes of protection. 
The dune areas covered with prairie grasses peculiar to the sand 
present different problems. As a general rule, there is sufficient 
organic matter in the surface six to eight inches to^ hold the sand 
particles. When the soil is cropped or pastured, some of this sur- 
face soil may be removed by the wind in exposed places, forming 



EOLIAL OR WIND-LAID DEPOSITS 



59 



what is called a "blowout"' (Fig. 56). The tendency is for this 
to increase in size and often results in ruining large areas. To 
reclaim these " blowouts " it is necessary to grow legumes, plants 
able to take their nitrogen from the air. The black locust (Fig. 57) 



0^k^ =■ 



•if**-^^'^ 



a 




Fig. 56. — Large "blowout" in sand area. Numerous small ones may be seen in the dis- 
tance. Mason County, Illinois 




Fig. 57. — Black locusts (Robinia pseudo acacia, L.), growing on sand to the right, drifting 
sand on left. (,L. A. Abbott.) 

is probably one of the best, although if the common sensitive plant, 
the partridge pea ( Cassia cliamcecnsta) , can get a start it will stop 
the movement. The trailing wild bean (Fig. 58) is another plant 
that grows luxuriantly on sand and does much toward building up 



60 



SOIL PHYSICS AND MANAGEMENT 



the soil. The particular advantage of this is that it reseeds itself 
aud follows rye and wheat with a good growth of renovating mate- 
rial. Bunch grass grows very well upon the blowouts and fre- 



y,^.Kd>'S9^.'-^i 




Fig. 58. — The trailing wild bean (Strophoslyles he.vola, Britton) makes a large 
growth that not only protects the sand against blowing but adds organic matter and nitro- 
gen to the soil. Illinois. 




Fig. 59. — Pines growing on sand dunes in England at Burry Port. (Carmarthen.) 

quently is the means of stopping the movement. The use of pines 
for this purpose is shown in figure 59. 

3. Loess. — Sand dunes are limited to regions where sand is 
abundant and where vegetation does not prevent its being moved. 



eOlial or wind-laid deposits 61 

It is never carried any distance by the wind but is rolled along the 
surface of the ground. Sand dunes rarely travel more than ten or 
fifteen miles. Finer material, however, may be picked up by the 
wind and transported for hundreds or even thousands of miles. 
This brings about a very wide distribution of the finer soil material. 
In many cases this is carried in sufficient amounts to form deposits 
several hundred feet in thickness. This fine deposit has been called 
" loess " by the Germans and tlie term is applied to the same deposit 
in this country. Loess is distributed over a large area in iSTorth 
America, comprising over 600,000 square miles, but is really limited 
to the states bordering the Mississippi Eiver and its tributaries. Its 
depth varies from, two to six feet over the principal part of this 
loess-covered area, but near the larger streams reaches a depth of 
25 to 150 feet. In Europe the loess is not so generally distributed as 
in North America, but occurs in somewhat isolated areas and seldom 
over 12 feet in depth. It extends, however, from northern France 
across Belgium, Germany, Austria, and southern Eussia, where it 
forms the soil known as the " black earth," or chernozem. It con- 
tinues eastward across Asia into China, where some of the deepest 
and most interesting deposits occur that are to be found anywhere. 
This deposit covers an area of 4:00,000 square miles in China, mostly 
in the basin of the Hoang Ho, in places to a depth of 1,500 to 2,000 
feet. It will be noticed that this belt follows the temperate zone. 
Loess deposits are found in Argentina and South Africa, but little is 
known of their extent. 

The origin of loess has been much discu'^sed and several theories 
have been advanced, but it is very likely that no one theory will 
account for the deposit in all cases. Since a careful study of the 
work of the wind has been made it is generally conceded that this 
agency is responsible for much the larger part of the deposit. There 
is little doubt but that some loess may have been deposited as a 
sediment from water and in some instances both wind and water 
have played a part. 

As evidence of its eolial origin, it is found at all altitudes up 
to 5,000 feet above sea level in Europe and probably as much as 
S,500 feet in the United States. To have this deposited by water 
would have required these regions to have been submerged to that 
extent and there is no evidence of such submergence. The depth 
of the deposit is quite uniform over hills and valleys as if it came 
like a gentle snow. In the United States, where the subject has 
received much attention, it is believed that the material has been 



02 



SOIL PHYSICS AND MANAGEMENT 



taken from tho ticKxi plains of streams that carried the "waters from 
the melting glaciers, depositing the rook lionr over the flooded 
plains of these streams (Fig. 60). During the cold part of the 
year the flood plains were bare and dry and this fine material was 
carried over the upland by the wind. The depth of the deposit 
varies with the width of the flood plain from which the material 
was derived and the distance from the stream. The coarser material 
was deposited on the npland adjoining the flood plain, while the finer 
was carried to much greater distances. Xear the flood plains from 
which it was derived it was occasionally deposited upon the uplands 




Fig. l>0. — AUxiviation by glacial sttvam bolow Hidden Glacier, Alaska. This occurred 
to a large extent during the Glaciivl Period. The upland loess was derived from these allu- 
vial deposits, vChatuberlain and SjUisbury, Courtesy Henry Holt & Co.) 

in the form of dunes, either as hillocks or ridges. These frequently 
show the typical dune topography. In Illinois and other states we 
find that along the larger streams the loess deposit is deeper on the 
Upland adjoining the wide bottom lands. AYhere no bottom land 
exists, the deposit on the adjacent upland is very thin. This indi- 
cates a very close relation existing between the loess and the bottom 
land. The deposit is deeper on the east side of the flood plains than 
on the west, indicating prevailing westerly winds at the time of 
deposition. Very much of the k^ss of Xortli America was deposited 
at the close of the lowan glaciation. The melting of this glacier 
seems to have been accompanied, as Leverett says, by heavy periodic 



EOLIAL OR WIND-LAID DEPOSITS 



63 



rainfall which caused floods that comiDletely covered the flood plains. 
These periods of alluviation were followed hy those in which the 
rivers contracted to their ordinary channels and left the sediment 




Fig. 02. — A road through a deposit of deep loess along the lower Illinois River. The deposit 
is 30 to 50 feet deep. The vertical walls are characteristic. 



u 



SOIL PHYSICS AND MAXACEMENT 



to dry. It Avas then pickinl up l\v iho wiiul and carried over the 
upland. Thiti lowan loess was very extensive, reaehing as far east 
as sonllnvesloru Oliio. north into \\"iseonsin. and as far south as 
Louisiana on hotli side-^ o( the Mississippi River. 

Loess is quite \init'orni in texture, eousistiug- printarily ol' par- 
ticles ol' silt mixed with line sand and a snuill amount of clay. Since 
u\uch limestone was ground up hy the glaciers, the loess contains a 
large proiunlion o( carhonates. as much as "-28 ]Kn- cent in some 
cases. The percolating carhonated water has dissolved the car- 
honate from the upper part and carried it downward, depositing it 
in the form of concretions of various sizes ami shapes as shown in 
tigure lU. Some of these are tuhular. It is prohahle that these were 
fornuHt in the openings left after roots had decayed. Concretions 
of iron' are fornuHl occasionally. 

The deeper loess deposits show characteristic vertical cleavage 
and cuts through this maintain vertical walls for long periods of 
time (Fig. i>v). Terrestrial shells, such as snails, are frequently 
found in the deeper deposits, with an occasional fresh water shell. 

The following table gives the analysis of loess from dilferent 
sources for comparison with a dust fall in Imliana: 



Physical Analysis of Loess and Dust * {Grades of Bureau of SoUs) 



Constituents 



Moisture 

Org5\nic matter. 

Gnwol 

Coarse saiui. . . . 
Modiuni siuul. . 

Fine sand 

Verv fine siviid. , 

Silt! 

Rne silt 

Clav 



Total. 



I'pland loess, i River loess, 
Virgiuia City, Virginia City, 



Illinois 



per cent 



0.(W 
0.01) 
0.00 
0.01 
7.t>8 

01.85 
O.liO 

15.15 



94.29 



Illinois 



per fivi/ 



0.00 
0.00 
0.01 
0.10 
24.84 
60.98 
2.S0 
6.15 



94.88 



Loess. 
Nebraska 



per ct»t 

5.40 
4.96 
0.00 
0.00 
0.00 
0.00 
23.14 
54.81 
2.46 
9.45 

99.22 



Dvist from 
snow, Rook- 
\-ille, Indiana 

per cffit 
3.17 

11.98 

o.w 

0.00 
O.lX) 
0.00 
0.00 
69. o 7 
5.80 
9.6S 

100.00 



The chemical analysis of live samples from different places is 
given in the next table. Note the amount of lime and magnesia. 
The deposit is usually characterized by a large amount of car- 
bonate. 



EOLIAL OR WIND-LAID DEPOSITS 



65 



Chemical Analyses of Loess from Various Sources * 



Constituents 



SiUca (SiOi) 

Alumina (AL2O3) 

Iron sesquioxide (FejOs) . . 

Iron protoxide (P'eO) 

Titanium oxide (Ti02).. . . 
Phosphoric anhydride 

(PsOs) 

Manganese oxide (MnO) . 

Lime (CaO) 

Magnesia (MgO) 

Soda (NazO) 

Potash (K2O) 

Water (H2O) 

Carbon dioxide (CO2). — 
Sulfurous anhydride (SOj) 
Carbon (C) 



Total. 



Galena, 
Illinois 



per cent 

64.61 

10.64 

2.61 

0.51 

0.40 

0.06 

0.05 

5.41 

3.69 

1.35 

2.06 

2.05* 

6.31 

0.11 

0.13 



99.99 



Kansas 

City, 
Missouri 



per cent 

74.46 

12.26 

3.25 

0.12 

0.14 

0.09 

0.02 

1.69 

1.12 

1.43 

1.83 

2.70* 

0.49 

0.06 

0.12 



99.78 



Vicksburg, 
Mississippi 



per cent 

60.69 
7.95 
2.61 
0.67 
0.52 

0.13 

0.12 

8.96 

4.56 

1.17 

1.08 

1.14* 

9.63 

0.12 

0.19 



99.54 



Valley 
of Iho 
Rhine 

per cent 

58.97 
9.97 
4.25 



Neubad, 
Switzerland 



11.31 
2.04 
0.84 
1.11 
1.37t 

11.08 



100.94 



per cent 

71.09 
16.78 



0.11 

'iisi 

None 
1.23 
1.30 
1.96 
0.80 



.87t 



97.95 



* Contains H of organic matter. 
t Organic matter dried at 100° C. 
i Ignition. 

3. Adobe, — Adobe is a calcareous clay of a gray, gray-brown 
or dull yellowish color, very fine grained and porous, friable and yet 
standing in vertical escarpments for many years. The adobe soils 
are found in the arid and semi-arid regions and represent both wind 
and water deposits. Much of the adobe was undoubtedly formed in 
shallow lakes by the deposition of very fine material which con- 
tained a large amount of carbonate, resembling loess in this respect. 
Professor Eussell ■' speaks of this deposit as assorted and spread out 
over the valley bottom by the action of ephemeral streams where it 
becomes mixed with dust blown by the winds from the neighboring 
mountains and rendered more or less coherent by the cementing 
action of carbonate of lime. It occurs from Mexico northward to 
Oregon and Idaho and from California to Colorado. In altitude it 
varies from sea level in Arizona to 8,000 feet and in thickness from 
a few feet to 3,000 feet or more. 

4. Volcanic Dust. — During the explosive eruptions of vol- 
canoes large quantities of dust and ashes are thrown into the air 
which may be carried long distances by the wind. Volcanoes 
existed formerly where no active ones are found at present. North- 
western United States was a region of great volcanic activity in 



66 SOIL PHYSICS AND MANAGEMENT 

comparatively recent gvologie time. As a result of this action, large 
deposits of volcanic dust are found in Washington, Oregon, Idaho, 
Montana, Wyoming, and Xebraska. In the latter state the deposit 
varies from -I to 30 feet in thickness, while in some of the north- 
"west«rn states the deposit is much deeper. To give some idea of the 
amount of dust that is transported by the Annd during a volcanic 
eruption, and the distance to which it may be carried, it is said that 
the dust from a volcano in Nicaragua was distributed by the wind 
over 1,500,000 sqtiare miles and that ashes from Krakatoa fell to 
a depth of several inches at a distance of a thousand miles from 
the volcano. 

QUESTIONS 

1. Give some examples of dust falls. 

2. Give classes of wind-laid material. * 

3. Where are siiiul dunes found and wliat is the source of the sand? 

4. What is the shape of sand dunes? How may they vary from this? 

5. How is sand movement stopped on the shores? 

G. HoAv may tixed dunes be ehangeil to wandering ones? 

7. What is a "blowout''? 

8. What special advantage does beach grass have for preventing drifting of 

sand? 

9. Where are loess deposits found? 

10. Give reasons for believing that loess is a wind deposit. 

11. Po dust particles carry a film of air? 

12. If so. what is the etl'ect of this on the specific gravity of the particle? 

13. What a*re some of the characteristics of loess? 

14. How does it compare Avith dust? 

15. Give characteristics of adobe. 
IG. Where is it found? 

17". How extensive are deposits of volcanic dust? 

REFERENCES 

^ I'ddeu. J. A.. Popular Science ^Monthly, September, ISSO. 

' Cort'ev, G. X.. Journal of Geology, vol. xvii. No. 8, 1900. 

^yicrrill. G. P.. Kocks. Rock-Weathering and Soils, p. 319. 

••Op. Cit.. p. 318. 

" Subaerial Deposits of Xorth America. Geol. ^Mag.. August, 1889. 

General Reference. — Free, F. F.. Bulletin OS. Bureau of Soils. U. S. 
D. A.. The Movement of Soil Material bv the Wind, with Bibliography. 



CHAPTER YI 

SOIL AND SUBSOIL 

The soil may be conveniently divided into two strata: (1) the 
top soil, consisting of (a) surface to 6% inches and (b) subsur- 
face 6% to 20 inches, and (2) subsoil, which extends to an indefi- 
nite depth, but is sampled from 20 to 40 inches. The difference 
between the two divisions, the top soil and subsoil, is mainly due to 
the action of organisms, both plants and animals, although physical 
and chemical agencies have played no inconsiderable part in pro- 
ducing these differences. 

1. The Top Soil. — (a) Surface. — The surface soil is confined 
to the part usually turned by the plow and is the stratum with 
which the farmer is most familiar. Organic matter and fertilizers 
are incorporated in this stratum and for this reason the roots of 
our common crops are largely confined here. The most obvious dis- 
tinction in m;ost soils between this and any other layers is the 
darker color produced by the larger content of organic matter or 
humus. This brings about decided color changes, such as darkening 
when moistened. Hydrated ferric oxide, if very abundant, may 
obscure the dark color of organic matter. 

The surface soil frequently differs from the other strata, and 
more particularly the subsoil, in being made up of slightly coarser 
material. This difference is not found in arid regions. It is due 
to the washing downward of the fine particles by percolating water, 
as well as by their removal through surface run-off during heavy 
showers. This stratum contains the largest amount of fertility but 
generally the least of lime. Organisms of all kinds, usually found 
in soils, are more abundant in this layer. Here are found the most 
favorable conditions for bacterial growth and activity. The germs 
of fungous diseases, if present in the soil, are more abundant in 
this stratum. It is the only part of the soil that we can change 
materially and hence its importance. 

(b) Subsurface. — The isubsurface stratum lies between the sur- 
face and the subsoil, but usually resembles the surface more closely 
than it does the subsoil. The stratum is a natural one, extending 
from the plowed soil to the line where the change in color, physical 
composition and structure indicates the beginning of the subsoil, 

67 



68 SOIL PHYSICS AND MANAGEMENT 

The thickness of this stratum varies from to 30 inches and even 
more, as in the case of peat and other swamp soils. That of normal 
upland loessial soils is from eight to ten inches. 

The amount of organic matter decreases with depth and varies 
with that of the surface soil. Under normal conditions it is never as 
abundant as in the surface because the root development is never 
so great and the chances for the introduction of other vegetable 
material are not so good. Exceptions sometimes occur in alluvial 
land. The same downward movement of fine material has taken 
place as in the surface soil, thus giving a slightly coarser texture 
than in the subsoil. The subsurface may be made of distinct layers 
that differ in color or texture or both. The color in prairie soil is 
usually due to organic matter, while in timber soils it is principally 
due to iron in some form. 

2. Subsoil. — The subsoil extends to an indefinite depth, l)ut is 
sampled to 40 inches in humid climates. This stratum is of great 
importance because drainage, capillary movement, root penetration 
and resistance to drouth depend largely upon its character, and this 
in turn depends largely u23on its origin. If residual, its character 
will vary with the parent rock from which it was derived. It will 
be uniform if the parent rock was massive, and variable if the 
parent rock was formed of strata of widely differing mineral and 
physical composition. In cumulose, lacustrine, glacial and alluvial 
deposits, the subsoil is likely to vary to almost any extent. There 
may be substrata of gravel, sand, silt, clay and even peat with all 
their variations. In loessial deposits two distinct layers usually 
occur in the subsoil, the upper from 6 to 15 inches thick consisting 
of a clayey silt or a silty clay, formed by the fine material carried 
downward from the upper strata by water and deposited in the 
upper subsoil, and the lower composed largely of silt and very fine 
sand, the very pervious ordinary loess. Subsoils are usually less 
pervious and more retentive of moisture than other strata. 

Tight Clay. — All soils in humid climates permit more or less 
water to percolate through them. When a rain falls water passes 
into the soil through cracks, burrows, along roots and through the 
pore spaces, carrying with it a small amount of very fine clay and 
some iron oxide to the depth of percolation. In time the deposition 
of this fine material between the coarser particles may produce a 
very heavy, dense stratum, reducing the pore space to such an extent 
as to make it almost impervious to air and water. This is especially 
liable to take place in acid soils where no lime is present to precipi- 



SOIL AND SUBSOIL 69 

tate or flocculate the suspended clay.! These tight' clay soils are 
found in ■ Southern Illinois, Missouri, Arkansas and many other 
places. 

The tight clay layer becomes very hard when dry, but when 
saturated with water it is very soft and posts may be driven into 
it easily. 

The tight stratum prevents underdrainage and the topography 
is almost invariably too flat for surface drainage. Damage to crops 
by water is very liable to occur. To remove the excess, plowing is 
done in small lands, the dead furrows are left open and by tliis 
means water may be removed, especially since these furrows are 
usually connected with a ditch at the end of the field. This tight 
stratum very seriously interferes with the capillary movement. The 
tight layer limits the storage of water to that part of the soil above 
it. Even if water is abundant below, it is cut off because the roots 
cannot penetrate this stratum and capillary movement through it is 
so extremely slow as to furnish but a scanty supply, with the result 
that crops are seriously affected l)y drouth. The effect of tight clay 
is very difficult to overcome. For the permanent improvement of 
soils of this kind, large applications of ground limestone, four to 
six tons per acre, with the growing of deep rooting crops, such as 
red, mammoth or sweet clover, are recommended. The jDuncturing 
of the tight clay by these roots will without doubt produce better 
conditions of drainage and aeration. Dynamite is sometimes used 
to break up the tight clay, but this method is too expensive for gen- 
eral farm use and besides the subsoil runs together again when 
.saturated. The loess beneath this tight clay, which is from eight 
to twelve inches thick, is ideal in physical composition. 

Hard Pan. — Hard pan proper is formed by the deposition of 
substances from solution around soil particles cementing them to- 
gether into a more or less stony mass. The deposition of this 
cementing substance is due, possibly, to the stoppage of percolation 
by an impervious stratum, evaporation brought about by some cause, 
or loss of carbon dioxide, causing precipitation, as in the case of 
lime carbonate. The cementing material is usually derived from 
the decomposition of rocks and may consist of such substances as 
iron, magnesia, liine or sodium carbonate and sodium chloride. 

Since the cause of hard pan is the stoppage of water in its 
movement downward the renewal of percolation will be sufficient 
frequently to destroy the hard stratum. If not too deep it may be 
broken with plow or subsoil plow, but if beyond the reach of these 



70 SOIL PHYSICS AND MAXAGEjNIENT 

implements dynamite must be resorted to. In planting trees on 
liardpan laud dynamite may be used aud thus allow the roots their 
usual penetration. If the hardpan is caused by sodium carbonate, 
it may be necessary to apply g^'psimi to destroy this carbonate and 
thus break up the hardpan. 

Humid and Arid Subsoils. — The subsoils of arid regions do 
not ditfer materially from the surface and subsurface because the 
fine particles are not moved downward to any extent by percolating 
water. In addition to this, soluble substances are present, which 
flocculate the collodial clay and prevent its movement downward. 
The arid subsoils do not possess the " raw "' or unproductive nature 
that characterizes the humid ones. In arid regions very deep plow- 
ing may be done immediately preceding the planting of the crop 
without detriment; in fact, it is of great benefit, because it allows 
deeper root penetration and greater moisture retention. In the 
process of leveling, preparatory to irrigating, the soil is sometimes 
removed to a depth of several feet without injurious effect on the 
crop that follows. In humid regions the farmer must be careful 
not to turn up much of the "raw" imweathered material. Just 
preceding time of planting the crop, but if deep plowing is done 
sufficient time should be given for the soil to " weather " before 
the crop is put in. This is probably partly due to biological 
conditions. 

The color differences do not obtain in the arid regions because 
the organic matter is derived almost entirely from roots, and these 
penetrate very deeply ; so there is no great accumulation of organic 
matter in the surface stratum. Oxidation of iron has not generally 
gone very fax because of lack of moisture, hence arid soils are not 
usually highly colored. 

Plow Sole. — Where plowing takes place at a somewhat uniform 
depth for a long time, the tramping of horses and the sliding action 
of the plow in the bottom of the furrow have a tendency to form a 
compact layer or plow sole. The washing of the fine material from 
the loose, plowed soil down on the furrow bottom tends to increase 
the tightness of the plow sole. In order to break up this stratum 
and prevent the formation of another, plowing should be done at 
variable depths, and when the moisture condition is such that pud- 
dling will not take plat^. 



SOIL AND SUBSOIL 71 

QUESTIONS 

1. What are the most obvious differences between the surface stratum and 

others ? 

2. What agencies have been instrumental in producing these? 

3. What are the upper and lower limits of the subsurface stratum? 

4. Under what conditions might the subsurface be absent? 

5. What difi'erences between it and the surface? 

6. Why is the subsoil of much importance? 

7. Upon what do the differences in subsoils largely depend? 

8. What is tlie origin of the tight clay stratum? 

9. Where are they found? 

10. Does limestone aid or prevent their formation? 

11. What are some objections to tight clay? 
12'. What are the methods of improvement? 

13. How is hardpan formed? 

14. How may hardpan be destroyed? 

15. Give differences in subsoils of humid and arid regions. 

16. What is meant by "raw" soil material? 

17. What effect does weathering have on subsoil? 

18. How do humid aiid arid soils differ in color? Why? 

19. How is a plow sole formed? 

20. What are the remedies for it? 



CHAPTER VII 

CLASSIFICATION OF SOILS 

Need of Classification. — The formation of soils by means of 
the various agencies described lias given rise to great coniiilexitj. 
As in any other natural group of objects, the study of the relation- 
ship existing between the different members of the group is neces- 
sary for a complete understanding of them. This brings about com- 
parison and classification. A very simple assumption would l^e that 
all soils derived from the same kind of rocks are the same. They 
do usually have some points of similarity, but so many modifying 
factors have been at work that important differences are produced 
even in these. It must be remembered that .soils are very complex 
bodies, due to the infinite variety of rocks from which they are 
derived and the large number of agencies taking part in their 
formation. 

By far the larger portion of soil material is moved from the 
place of its origin for varied distances, perhaps hundreds of miles. 
In its travels it may be deposited over and over again, and as a 
general rule the loose surface of the earth is a mass of drifting 
material, here to-day and a hundred or even a thousand miles from 
here in the next geological age. 

BASIS OF CLASSIFICATION 

1. Geological. — Soil is a geological formation derived from 
rocks by geological forces. It is very natural, then, that the geo- 
logical formation should be used as the basis of classification. A 
number of States have made general soil maps, basing the areas 
upon the geology. In many cases this may serve a good purpose, as 
where the soils are closely related to the underlying geological for- 
mation. In other places the same formation may give rise to a 
great variety of soils, and in this case a classification on a geological 
basis would mean nothing. In extensive glaciated regions the soil 
usually bears little or no relation to the geological formations 
beneath the drift. General soil divisions may be based upon the 
geological agencies that have produced them, and in this way form 
an important factor in classification. This gives rise to residual, 
glacial, loessial, alluvial, and other formations. 
72 



CLASSIFICATION OF SOILS 73 

2. Lithological.^ — In many cases soils have been classified 
according to the rocks from which they have been derived or upon a 
lithological basis. Eocks of the same name are so different in com- 
position aiid are exposed to so many and such varying conditions 
and agencies of change that they may give rise to very different 
soils. A soil derived from a granite may be very fertile under one 
set of conditions or almost absolutely sterile under another. 

3. Temperature. — Besides breaking down rocks into soil mate- 
rial and aiding solution slightl}^, heat does not play such an impor- 
tant part directly in the formation of soil, but indirectly through 
its effect and influence upon other agencies, temperature is of the 
greatest importance. Moderately high temperatures influence the 
growth of j)lants and bacterial action as manifested in oxidation 
and humification of organic matter. This brings about most impor- 
tant physical, chemical, and biological differences. On the basis 
of temperature soils may be divided into (a) tropic, (b) sub tropic, 
(c) temperate, (d) subarctic, and (e) arctic. These are only very 
general and have but little significance in a system of classification. 

4. Moisture. — Moisture is not only a very important factor in 
breaking down rocks into soil material, but it brings about very 
fundamental changes in the soils themselves, both chemically and 
physically. The presence of moisture is necessary for all chemical 
changes, hence decomposition of minerals can take place onl}^ when 
water is present. It is usually accompanied by the formation of 
soluble compounds that are leached out and carried away, and fre- 
quently to such an extent as to leave the soil deficient in plant food. 

Soils are sometimes divided into arid, where the annual precipi- 
tation is less than 10 inches; semi-arid, 10 to, 20 inches; sub-hwmid, 
20 to 30 mches; humid, more than 30 inches, and super-humid, 
including swamps. There can be no distinct line of difference 
between the soils of such groups. In some parts of India, with 
a rainfall of 28 inches, the conditions are extremely arid because the 
rainfall comes in, a .very few months and as torrential showers, 
resulting in much loss by run-off. The evaporation is very great 
during the rest of the year. In parts of Texas, with a rainfall of 
30 inches, it is much more arid than in North Dakota with the same 
rainfall, because of the character of the rainfall a,nd the greater 
evaporation in the former. 

Great differences exist between soils of arid and humid regions, 
primarily due to the amount of rainfall. The moisture as, .well as 
the temperature influences the amount and character of organic 



74 



SOIL PHYSICS AND MANAGEMENT 



matter in soils. The presence of water in large amounts arrests 
decomposition, as in swamps, by excluding oxygen, while its presence 
in moderate quantities stimulates nitrification in drained land. In 
its movement downward through a soil, water not only carries 
soluble compounds with it, but moves the fine particles downward, 
thus producing differences in physical composition in the different 
strata. 

(a) Arid Soils, — ^The agencies of disintegration predominate 
over those of decomposition in arid regions As a result the soils are 
characterized by large amounts of original minerals that have been 
changed very little. 

Mineral Content of Soils * 



Region 


Number of 
samples 


Minerals other than quartz 
in the 




Sand 


Silt 


Arid 


30 

40 
160 


per cent 

37 
20 

8 


per cent 

39 


Prairie (subhumid and humid) 

Timber (himiid) 


29 
12 



The great agency in chemical changes of rocks is water, and its 
deficiency in arid regions has protected the minerals from those 
profound changes that take place in humid regions. The minerals 
have been broken do"uai into rather fine material, but not into clay, 
which results largely from decomposition. Silt and various grades 
of sand predominate. Their mineral content is indicated in the 
above table. 

The low rainfall renders any large amount of leaching impos- 
sible, so that the soluble salts formed during the limited decomposi- 
tion remain in the soil. They may be moved downward to some 
extent by the water, but when evaporation takes place they are 
brought to the surface again. If excessive evaporation occurs these 
salts may be brought to the surface in sufficient quantities to be 
quite injurious as " alkali." 

Soluble Salts in Soils * 



Arid 

Prairie (subhumid and humid) 
Timber (humid) 



Per cent 



0333 
0.048 
013 



CLASSIFICATION OF SOILS 



75 



Although somewhat easily soluble, lime is a very abundant con- 
stituent of soils of arid regions. The amount varies from 0.69 to 
5.66 per cent. The table below gives the average for arid and humid 
soils. 

Lime and Magnesia in Soils of Different Regions ' 





Number of 
samples 


Per cent 




Lime (CaO) 


Magnesia 
(MgO) 


Arid 


318 
215 

743 


2.65 

1.09 

.41 


1.20 


Prairie (subhumid and humid) 

Timber (humid) 


.51 
.37 



These arid soils are generally gray or light in color, with no very 
decided change in texture in the subsoil. The rainfall is not suffi- 
cient to carry the fine material downward in any large amount. 

The organic-matter content of arid soils is generally low, 
although it contains a larger percentage of nitrogen than the organic 
matter of humid regions. 

(b) Humid Soils. — In tliis group of soils the agencies of 
decomposition have predominated over those of disintegration. The 
feldspar and many other minerals have largely undergone chemical 
change, producing the finer soil constituents. Hence the soils con- 
tain large amounts of clay. The subsoil differs quite noticeably in 
texture from the surface. Leaching has done very effective work 
in removing soluble salts, as shown by the second table on page 74. 
Limestone has been leached out, and most of the soils are acid and 
in great need of this most important constituent. The colors are 
more highly developed, due to the greater oxidation of iron and the 
larger amount of organic matter. 

5. Vegetation. — Kot only do bacteria, fungi, and algae play a 
very important part in soil formation and soil changes, but the 
higher plants, especially grasses and trees, exert a most important 
influence upon soil in several ways. They are responsible to a very 
large extent for the amount of organic matter in soils. The char- 
acter of the vegetation has given rise in humid and subhumid 
regions to two great groups of upland soils, (a) prairie, and (b) 
timber (Fig. 63). 

(a) Prairie Soils. — Prairie soils are usually characterized by a 
dark color, due to a large content of organic matter. The prairies 
were covered with a rank growth of grasses which produced a dense 



76 



SOIL PHYSICS AND MANAGEMENT 



network of roots whose partial decay has provided the soil with an 
abuiidaiiee of organic matter. This extends to a depth of 13 to 24 
inches in amounts sutfieient to impart the predominating dark color. 
The prairie soils contain a larger amount of lime than the timber 
soils, and this may be one important factor in their origin. They 
usually give an alkaline or neutral reaction. An exception to tMs 
is found in Southern Illinois, some parts of Missouri, and Arkansas. 
These prairies are acid and have a tight clay or so-called "hardpan " 
subsoil. 

Prairie §oils have had sufficient rainfall to leach out the larger 








i Rocty ^ounrain Forest 
I Southern forest 
I Cent ml Forest 
I Foci fie Coast forest 



■llfe^'^-^- 






^5k 



■^H tJcrthern Fonsst 

rt SJ Sub-Trcfucal cina Tropical forest ' 



Fig. 63. — Map of Unit-ed States, showing timber and prairie areas. Unshaded area, 
Prairie. Dark shade in Northeast and North, Central forests. Lighter shaded area in South- 
east, Southern forests. Very lightly shaded area. Rooky Mountain forests. Deep shade. 
Pacific Coast forests. (Graves, U. S. D- A. Forest Service. 1 

part of the soluble salts, so that aJkali is found only in small areas, 
and then consists principally of the more insoluble magnesium car- 
bonate. The second table on page 74 shows 0.048 per cent of solu- 
ble salts in prairie soils, as compared with 0.013 for timber soils. 

The prairie soils extend from Southern Texas northward into 
Canada, widening to the east into west central Indiana. A belt which 
is not shown in figure 63 extends across Mississippi and Alabama 
and over into Texas. 

( h ) Timber Soils. — The timber soils are characterized by a 
lighter color, due to a small amount of organic matter. This has 



CLASSIFICATION OF .SOILS 77 

been brought about by the growth of forests, which place large quan- 
tities of organic matter, as leaves and twigs, on the surface of the 
soil, yet very little becomes incorporated in it. This material either 
completely decays or is burned by forest fires. The resulting soils 
are light colored. 

The relatively heavy rainfall on timber soils has leached out tlie 
soluble material, including limestone, so that they are neutral or 
acid. It is likely true that the leaves have aided in this process. 

6. Color. — One of the most important factors in distinguishing 
soils is that of color. This is primarily due to two things, organic 
matter and compounds of iron. Color is a fair indication of the 
value of a soil. If a large amount of organic matter is present the 
soil will be black or brown, while a smaller amount may be obscured 
by the more highly colored iron compounds. Dark brown or black 
soils are usually fertile. The color imparted by iron compounds 
varies with the degree of oxidation. 

7. Texture. — The size of the soil particles and the proportion 
of each grade are the most important factors in grouping soils into 
classes and tj^pes. 

QUESTIONS 

1. Why are soils so complex? 

2. Why should the geological formation be used as the basis of classifi- 

cation ? 

3. What is the value of a soil map based upo,n the geological formation? 

4. Are all soils, derived from the same class of rocks, the same? Why? 

5. What part does heat play in forming soils? 

6. Wliat is the significance of moisture in soil formation ? 

7. What are the divisions of soils based on moisture? 

8. Why may Texas with a 30-inch rainfall be more arid than North Dakota 

with 20 inches ? 

9. What eft'ect does heavy rainfall have on organic matter? 

10. What agency predominates in the formation of soils of arid regions? 

11. Why do humid soils have a larger percentage of quartz than arid soils? 

12. Why are arid soils gray or light in color? 

13. What agency is most active in the formation of humid soils? 

14. Why do arid soils have large amounts of carbonates? 

15. Why are humid soils more highly colored than arid ones? 

16. Explain the source of organic matter of soils. 

17. Give diff"erences between timber and prairie soils. 

18. Locate the large prairie region of the United States. 

19. Why do the heavy forests add so little organic matter to the soils? 

20. What is the significance of color in soil classification? 

21. What is meant by texture of a soil? 

REFERENCES 

'Coff'ev. G. N., A Studv of the Soils of the United States, Bulletin 85, 

Bureau of Soils, U. S. D. A., p. 15. 
='0p. Cit. p. 15. 
«0p. Cit. p. 14. 



CHAPTEE VIII 

CLASSIFICATION BY THE BUREAU OF SOILS 

Thp] results of all the preceding factors involved in soil clianges 
find expression and application in the system of classification devel- 
oped by the Bureau of Soils. The United States has been divided 
into 13 great geographic divisions ; the six in the western part are 
known as soil regions, while the seven in the eastern part are called 
soil provinces. 

A soil province is an area which has the same general physio- 
graphic expression and in which the soils were produced by the same 
forces or groups of forces. 

A soil region may include several soil provinces which later 
study may establish. The soils of a province are grouped together 
into series on the basis of the same range of color, the same character 
of subsoil, as regards color and structure, the same type of relief 
and drainage, and a common or similar origin. A soil series is 
divided on the basis of texture into classes. 



Soil Provinces and Regions. — Area Surveyed up to 1915 



Provinces 



Piedmont Plateau 

Appalachian Mountain and 
Plateau 

Limestone Valley and Up- 
land 

Glacial and Loessial 

Glacial Lake and River 
Terrace 

Atlantic and Gulf Coastal 
Plains 

River Flood Pliiins 

Regions 

Great Plains 

Rocky Mountains 

Northwest Intermountain . 

Great Basin 

Arid Southwest 

Pacific Coast 

Total 

78 



Estimated 
area 



acres 

47,214,000 

84,837,000 

67,870,000 
385,083,000 

442,788,000 

218,362,000 
75,247,000 

331,968,000 
265,575,000 

75,984,000 
118,034,000 

81,148,000 
109,180,000 



Detailed 
survey 



acres 

16,638,950 

19,643,709 

11,660,094 
43,475,366 

12,956,602 

52,718,882 
26,913,813 

13,170,106 
2,674,560 
2,322,884 
1,399,072 
1,674,138 

16,953,491 



1,903,290,000 I 222,201,667 



Reconnais- 
sance survey 



2,388,416 

23,509,504 

2,040,896 
37,724,608 

'", 197,728 

22,748,096 
7,561,216 

127,711,616 



46,080 
4,015,360 



234,043,520 



Total 
area 



per cent 

40.3 

50.8 

20.2 
21.1 

45.0 

34.6 
45.9 

42.4 

1.0 

3.06 

1.18 

2.10 

19.2 



23.9 



CLASSIFICATION BY THE BUREAU OF SOILS 79 

A soil class includes all soils having the same texture, such as 
clays, peats, mucks, clay loams, etc., and are divided into soil types. 

A soil type is a soil which throughout the area of its occur- 
rence has the same texture, color, structure, character of subsoil, 
general topography, processes and sources of derivation. 

The soil surveys are of two kinds, reconnaissance and detailed. 
The former furnishes only general information, while the latter 
gives the soil types in considerable detail. 

I. THE PIEDMONT PLATEAU PROVINCE 

The Piedmont Plateau comprises the rolling to hilly region 
lying between the eastern foot of the Appalachian Mountains and 
the Atlantic Coastal Plain. The northern end of this province lies 
in northeastern New Jersey, along the glacial boundary, in the 
vicinity of the Hudson River. It extends southwestward, and in 
Virginia is a belt ranging from 20 to 50 miles in width. Widening 
here it continues in a southwesterly direction to central Alabama 
with an average width of approximately 115 miles. The province 
has a length of 900 miles, and embraces an area of approximately 
73,770 square miles. The following are the most important series 
of this province : 

Alamance Series. — The surface soils of this series are gray to 
almost white and of silty texture. The subsoils are composed of 
yellow, rather compact silty clay. Scattered over the surface are 
fragments of the parent rocks which belong to the " Carolina 
slates." It forms a belt in central North Carolina, and extends a 
short distance into South Carolina. The topography varies from 
nearly flat to rolling, or in some places steeply rolling. 

Cecil Series. — The Cecil series include the most important and 
widely distributed soils of the Piedmont Plateau. The heavier 
members are known as the " red-clay lands." These soils are 
residual, derived from gneisses and schists and characterized by 
their red-clay subsoils and gray to red soils, ranging in texture from 
sand to clay, the lighter colors prevailing in the sandy members. A 
characteristic of the subsoil is the content of sharp quartz sand and 
the frequent occurrence of the remains of veins of quartz. Mica 
flakes are also usually present in the subsoil. The topography is 
slightly rolling to hilly. The soils are adapted to general farm 
crops and in the South to cotton. Over seven and one-half million 
acres have been mapped. 



80 SOIL PHYSICS AND MANAGEMENT 

Chester Series. — The Chester series occurs iu the northern part 
of the Piedmont Plateau^ having heen mapped only in Pennsylvania, 
Maryland, and Virginia. The types in this series differ from those 
in the Cecil series in having yellow or only slightly reddish yellow 
subsoils and gTay or brown surface soils, the latter being, on the 
whole, lighter and more friable than the Cecil. Locally they are 
known as '' gray lands," to distinguish them from the " red lauds " 
of the Cecil series. The soils are adapted to general farm crops 
and fruit. 

Durham Series. — The soils of the Durham series are character- 
ized by the grayish color of the surface and the yellow color of the 
subsoils. They are derived from light-colored, rather coarse-grained 
granite and gneiss, consisting principally of quartz and feldspar, 
with some mica. 

Iredell Series. — The soils of the Iredell series are light brown 
to almost black in color and frequently carry small iron concretions. 
The subsoils consist of extremely plastic, sticky or waxy clay of a 
yellowish brown to greenish yellow color. Disintegrated rock is 
often encountered within the three-foot section. The soils are best 
suited to grain and grass. 

Lansdale Series. — The Lansdale series is characterized by the 
gray, drab, or brownish color of the soils and by the slaty gray to 
pale yellowish color of the subsoil. They are derived from metamor- 
phosed Triassic sandstone and shale. ^Moderate yields of hay, corn, 
oats, wheat, and Irish potatoes are secured. 

Louisa Series. — The soils of this series are predominantly gray 
to ligbt gray and the subsoils red. The material is derived from 
talcose and micaceous schists and imperfect crystalline slates. They 
are suited to corn, grain, forage crops, and cotton. 

Manor Series. — The ]\Ianor soils are characterized by their yel- 
lo^nsh-brown to brown surface color and the yellow to yellowish- 
red or dull red color of the subsoils. This series is also high in mica 
in both soils and the subsoil. They are derived from mica and 
chlorite schists.- Good yields of corn, wheat, oats, Irish potatoes, 
and hay are obtained. 

Penn Series. — The Penn series includes Indian-red soils derived 
through the processes of weathering from red sandstones and "shales 
of Triassic age. Detached areas of these rock formations occur in 
sha;llow basins in the Piedmont Plateau from the vicinity of ISTew 
York to Soutb Carolina. Corn, wheat, oats,- potatoes, grass, apples, 



CLASSIFICATION BY TPIE BUREAU OF SOILS 81 

and peaches are produced in the northern and tobacco and cotton in 
the southern states. 

York Series. — The types included in the York series are pre- 
dominantly gray to light gray at the surface and have yellow sub- 
soils. They are derived from talcose and micaceous schists an3 
imperfectly crystalline slates. Crop yields are usually low and the 
soils are exceedingly difficult to improve. 

II. THE APPALACHIAN MOUNTAIN AND PLATEAU PROVINCE 

This province embraces three subdivisions of the Appalachian 
system, which extend from New Jersey and northern Pennsylvania 
to central Alabama. They are as follows : ( 1 ) The Blue Ridge 
region on the east and southeast side; (2) The Cumberland- Alle- 
gheny plateau on the west; and (3) the Appalachian ridge and 
valley belt between. The province includes ,two subordinate divi- 
sions lying outside of this general area : ( 1 ) the Ouachita and 
Boston mountain ridge of the Ozark uplift west of the Mississippi 
River, and (2) the area of Coal Measure rocks in western Ken- 
tucky and southern Indiana. The Appalachian constitutes the 
greater part of the province and forms a broad belt approximately 
900 miles long. It includes the mountains, ridges, and valleys of 
this area. This province is about 200 miles wide in Pennsylvania 
and attains a maximum breadth of about 270 miles in Virginia. 

Berks Series. — The soils of the series are yellowish-brown' to 
brown with yellowish subsoils. The soils are 'derived from the 
Hudson River shales, which are yellow, brown, grayish, and olive- 
colored. They occupy rounded ridges and hills with good drainage. 
They are suited to corn, oats, wheat, and Irish potatoes. 

Conasauga Series. — The Conasauga series are light brown, and' 
the subsoils are yellow and prevailingly of "silty clay loam to silty 
clay in texture. These soils are developed typically in flat to gently 
rolling valley lands. They are derived from interbedded shale, lime- 
stone, and fine-grained sandstone. Good yields of cotton, corn,' 
wheat, oats, and forage crops may be secured. ' " ' 

De Kalb Series. — The surface soils of this series are gray to'' 
brown, while the subsoils are commonly some shade of yellow"; T^'he" 
soils are derived, from the disintegration of sandstone^ alid shalfes.' 
The surface features consist "of gentiy rolling table' lahrls, hills, arid 
mountains. The soils are generally not' very pT^oductive,' brit the 
stony and sandy members are adapted to orchard fruits, while the 
6 



82 . SOIL PHYSICS AND MANAGEMENT 

heavier ones produce hay and pasture gr^ses. Sixteen million acres 
of this series have been mapped. 

Fayetteville Series. — This series consists of grayish brown to 
brown soils with yellowish brown to reddish brown subsoils. The 
soils are formed by the weathering of sandstones and shales and are 
found throughout a large part of western and northwestern Arkan- 
sas and eastern Oklalioma. They are moderately fertile. 

Hanceville Series. — The Hanceville series has a light brown to 
reddish brown surface and a red subsoil. The topography ranges 
from rolling to steeply rolling. The soils are derived from sand- 
stones and shahs and are moderately productive. 

Meigs Series. — This series is variable in character and particu- 
larly in color, which ranges from Indian red to gray or pale yellow. 
The -soils are derived from red, fine-grained sandstones and shales 
and from grayish sandstone and shales. The topography is steeply 
rolling. The soils are suited to grass and the production of hay. 

Porters Series. — This series includes the residual soils of the 
Appalachian mountains derived from igneous and metamorphic 
rocks. They occur at high elevations. The soils are particularly 
adapted to fruit culture. 

Talladega Series. — The soils of this series are grayish bro^ni to 
light brown. The subsoils are red and have a greasy feel. The soils 
are derived from metamorphic rocks, principally micaceous schists. 
The topography is strongly rolling to moimtainous. They give 
moderate yields of corn, forage crops, and cotton. 

Upshur Series. — In the Upshur series both soils and subsoils 
are Indian red. Some types have the grayish to grayish-red color 
in the surface soils. They are derived from Indian-red sandstones 
and shales, frequently of calcareous nature. They occupy rolling 
to mountainous regions. They are generally more productive than 
the De Kalb series. 

Westmoreland Series. — This series is marked by the grayish 
brown to yello'vnsh brown color and mellow structure of the 
surface soils and the yellowish brown to yellow color and friable 
structure of the subsoils. The soils are derived from shales and 
sandstones, with interbedded limestones and calcareous shales. The 
topography ranges from gently sloping to quite rolling or steep 
lands. These soils are very productive, being particularly adapted 
to corn, oats, wheat, grass, potatoes, apples, peaches, plums, cher- 
ries, berries, and vegetables. 



CLASSIFICATION BY THE BUREAU OF SOILS 83 

III. LIMESTONE VALLEYS AND UPLANDS PROVINCE 

This i^rovince includes two important topographic divisions — • 
the limestone valleys and uplands. The limestone vallej^s are most 
extensively developed within the Appalachian Mountain System, 
and besides these the Central Basin of Tennessee and the bluegrass 
region of Kentucky. 

The uplands division includes a large area extending from 
Alabama through Tennessee and Kentucky almost to the Ohio 
Eiver. The Ozark region of southern Missouri, northern Arkansas, 
northeastern Oklahoma, and southeastern Kansas is included. 

The principal soil series are as follows : 

Brooks Series. — The soils are grayish brown to brown with 
yellowish brown to slightly reddish brown clay subsoils. The soils 
are derived from pure limestones, with an occasional admixture of 
material from associated sandstone and shales. These soils have 
good drainage. Wheat, corn, oats and apples do well. 

Clarksville Series. — The soils are gray and the subsoils yellow 
and usually silty clay in texture and frequently underlain by a 
reddish substratum. The depth to red material varies with the 
topography, being deeper on the more level areas. The soils are 
derived from a cherty limestone and occur over both level and un- 
dulating uplands and rough and hilly country with steep slopes. 
They are adapted to tobacco, grass, small grains, corn, strawberries 
and cantaloupes. Over five million acres have been mapped. 

Colbert Series. — The surface soil is grayish to light brown and 
the subsoil yellow and frequently plastic. The series is derived 
from pure limestone or a limestone mixed with sandstone. The 
topography is flat to undulating and drainage is generally poorly 
established. With proper drainage wheat, oats, corn, and forage 
crops can be grown with good results. 

Conestoga Series. — These soils are yellowish brown to brown. 
The subsoils are yellow greenish, occasionally mottled with gray, 
and have a greasy feel. These soils are derived from schistose lime- 
stone and calcareous shale or shaly limiestone. They are adapted 
to general farm crops. 

Decatur Series. — The soils are characterized by a reddish 
brown to deep red color and subsoils by an intensely red or blood 
red color. They are derived mainly from pure limestone, with some 
traces of chert, and are adapted to corn, small grains and forage 
crops. They occur as nearly level to gently rolling valley lands. 

Hagerstown Series. — The soils of this series are prevailingly 



84 SOIL PHYSICS AND MANAGEMENT 

bro^ra iii color, with light browu to reddish brown subsoils, but 
never so distinctly red as the Decatur series. The topography is 
undulating to gently rolling. They are derived from limestone. 
The soils are very productive and well adapted to corn, small grain, 
clover, blue grass, timothy, and apples. Three million acres have 
been mapped. 



lY. THE GLACIAL AN^D LOESSIAL PROVIXCE 

The glacial and loessial province includes that part of the United 
States lying east of the Great Plains in which the soils are derived 
from (1) ice-laid deposits left by the retreat .of the ice at the close 
of the glacial period, (2) Avater-laid material intimately associated 
with the ice-laid material, deposited during the advance and retreat 
of the ice in the form of out- wash plains, and (3) silt deposits laid 
down by water or wind during, or subsequent to, the retreat of the 
ice. The ice-laid deposits are found north of an irregular line run- 
ning from Cincinnati to La Crosse, Wisconsin, thence southward 
to Iowa City, Iowa, continuing in a westerly direction to the south- 
eastern corner of South Dakota. South of that line they are mainly 
loessial, presumably wind-laid deposits. The two tongues, the one 
running down the Mississippi and the other southwestward across 
Kansas and Oklahoma, are entirely so. 

Bangor Series. — This series is characterized by grayish to yel- 
lowish brown surface soils, with subsoils of lighter gray and yellow- 
ish brown. All of the types are stony and gravelly. The soils are 
derived from glacial till containing more or less material from the 
local serecitic schist rock. The topography is rolling to hilly. With 
the exception of the stony loam and shallow phase of the loam the 
tv'pes of this series are fair general farming soil. 

Caribou Series. — The members of this series have yellowish 
brown soils which usually rest upon a light gray lower till. The 
soil material is derived from glacial till overlying calcareous shales 
or shaly limestone, the till itself being derived from the under- 
lying calcareous formation, having been transported for only short 
distances. - The soils are very productive, being especially adapted 
to Irish potatoes, grain and peas. 

Carrington Series. — These soils are derived through weather- 
ing of the glacial till with little or no modification from loessial de- 
posits. The soils are generally prairie, black in color, ranging in 
some cases to dark brown. The subsoils are lighter colored gen- 



CLASSIFICATION BY THE BUREAU OF SOILS 85 

erally, having a liglit brown or yellowish color. The topography 
is gently undulating to rolling. Corn and wheat are the principal 
crops grown. Nearly four million acres have been map^^ed. 

Cazenovia Series. — These soils are brown in color with a brown 
to reddish subsoil resting on limestone at a depth of about 3 feet. 
Fragments of limestone and. red sandstone are found throughout i 
the soil and occasionally large boulders are scattered over the sur-^ 
face. These soils are derived from glacial till containing consid- 
erable limestone material. The principal crops are grass, alfalfa/ 
corn, wheat, and potatoes. 

Coloma Series.— The soils of this series are light brown to 
grayish in color with yellow or reddish subsoils. The topography- 
is generally rolling to rough and hilly, representing terminal and 
ground moraines. The series is formed from relatively coarse 
glacial material modified to some extent by the action of the wind 
and water. They once supported extensive pine forests and are 
found in northern Michigan, Wisconsin, and Minnesota. Nearly 
two and one-half million acres have been mapped. 

Cossaymna Series. — These soils are brovm or. snuff colored, 
with subsoils of the same color, but of a lighter shade. Both strata 
contain considerable quantities of shale and calcareous sandstone 
fragments with a small percentage of foreign boulders. They are 
derived from glacial till and occupy rolling to hilly uplands. The 
principal crops are corn, oats, hay, potatoes, apples and other 
tree fruits. 

Dutchess Series. — The Dutchess soils are brown to light brown 
with bluish, light brown, yellowish or reddish brown subsoils. The 
soils are friable, the su):)soils l)eing somewhat heavier in texture 
than the soil. In some types rounded and, angular gravel occur in 
both soil and subsoil. These are rarely of limestone. The to- 
pography is rolling to undulating and rough. The soils are adapted 
to oats, grass, potatoes, and tree fruits. 

Flushing Series. — The soils are brown in color and overlie yel-- 
lowish or reddish subsoils, sometimes micaceous and in some in- 
stances resting on crystalline rock. The material is of glacial origin. 

Gloucester Series. — The soils of the Gloucester series are light, 
brownish or often grayish at the immediate surface and overlie yel- 
low subsoils. The soils are derived from a rather local glaciatiou' 
of crystalline rocks of granites and gneiss. The drainage is fair 
to good. The topography ranges from gently undulating to rollings 
or hilly. Scattered rocks and boulders of large size occasionally 



86 SOIL PHYSICS AND MANAGEMENT 

occur, rendering the use of farm macliinery somewhat difficult. 
They give fair yields of corn, potatoes, oats, hay, and fruit. 

Holyoke Series. — The soils are brown to dark yellow in color. 
The subsoils are yellow and somewhat heavier than the soils. They 
are of glacial origin and derived from metamorphic, diabase and 
crystalline rocks. The topography is rough and the soils are mod- 
erately productive. 

Kewaunee Series. — This series is characterized by grayish to 
reddish brown or pinkish soils overlying pinkish red silty clay and 
rather calcareous subsoils. They are derived from till and contain 
more or less angrilar pebbles. ' The topography varies from undu- 
lating to hilly, but the underdrainage is generally poor. 

Knox Series. — These soils are light brown and are derived from 
loessial or other wind blo-\Am deposits. The topography is gently 
undulating to rolling. Grain crops constitute the chief agricultural 
products. About three million acres have been mapped. 

Lackawanna Series. — These soils are derived from glacial drift 
that forms a relatively thin mantle overlying the red shales and 
limestones. The topogTaphy is slightly rolling to hilly and moun- 
tainous. 

Lexington Series. — Lexington soils are gray to yellowish gray 
in color and mellow in structure. The subsoil is yellow to brown, 
with a tinge of red in places, and is often somewhat heavier than 
the soil. Drainage is good and the topogi-aphy is moderately rolling 
to hilly. The types are derived from loess with orange sand a few 
feet below the surface. These soils are adapted to corn, cotton, 
forage crops, vegetables, and strawberries. 

Marion Series. — These soils are gray, white or ash colored. 
The subsoils are white at the top, the white layer varying in thick- 
ness from 2 to 12 inches and averaging about five inches. This 
layer is compact, impervious, whitish silt or very fine sand, often 
containing iron concretions and locally known as "hard-pan.'' Be- 
neath this the true subsoil is a gray, light yellow to reddish yellow or 
mottled brownish yellow, hard, impervious clay containing occa- 
sional concretions of iron and lime. The topography is flat to un- 
dulating. Drainage is poor. They are derived from modified loess. 

Marshall Series. — The Marshall series includes the dark col- 
ored upland loessial soils which predominate in the great prairie 
region of the central west. The surface soils have a dark brown 
to black color. The topography is level to rolling and artificial 
drainage is usually necessary to secure best results. They are very 



CLASSIFICATION BY THE BUREAU OF SOILS 87 

productive and constitute the great corn soils of the country, 
Nearly four million acres have been mapped. 

Memphis Series. — The Memphis series is characterized by the 
light brown to yellowish brown color and silty texture of the sur- 
face soils and by the slightly lighter colored and more compact 
structure of the subsoils. They occur south of the latitude of St. 
Louis and are most extensive in the loessial belt following the 
east bank of the Mississippi river. Erosion has been active and 
has resulted in a prevailingly rolling to broken topography. They 
are well suited to corn, oats, peanuts, forage crops, and cotton. The 
amount mapped is 2,000,000 acres. 

Miami Series. — The soils are brown, light brown or grayish 
and are underlain by yellowish and brown heavier textured soils. 
Mottlings of brown and light gray are present in the subsoils. Sur- 
face drainage is usually good. The soils in the main are derived 
from the weathering of glacial till composed largely of ground-up 
limestone. Dairying is an important industry on the heavier types. 
Nearly four million acres have been mapped. 

Mohawk Series. — The Mohawk soils consist of dark colored 
glacial material derived in part from dark colored calcareous shales 
and limestones, but modified by admixture of glacial till from other 
formations. The topography is rolling to hilly and they are con- 
sidered good general farming soils. 

Ontario Series. — These soils are brown to chocolate brown in 
color, the subsoils being lighter and in many cases grading into 
yellow. Both soil and subsoil usually contain scattered fragments 
of limestone and are derived from glacial till of the drumlin region 
of New York. The topography is undulating to hilly. 

Plymouth Series. — These soils are derived from moderately 
coarse glacial material largely from granites. The series includes 
the morainal and till deposits found in southeastern New England 
and on Long Island. The surface soil is shallow and brown, under- 
lain by a pale yellow subsoil. 

Putnam Series. — This series includes dark gray to black soils 
overlying impervious drab or brown subsoils of fine texture and close 
structure. One of its principal characteristics is the presence of a 
whitish silty layer between the soil and the subsoil. The soils 
occupy level to gently undulating prairies and are derived from 
loessial deposits. Drainage is poor because of the dense compact 
structure of the subsoil. They are confined to Missouri. 

Richland Series. — The Richland series is characterized by a 



88 SOIL PHYSICS AND MANAGEMENT 

light brown to yellowish brown color and silty texture of the sur- 
face soils and the somewhat lighter color and more compact struc- 
ture of the subsoils. These soils are derived from the loess and 
occur in association with the jMemphis soils. The topography is 
smooth, flat to undulating. Cotton, corn, peanuts, oats, forage 
crops, clover, cabbage and Irish potatoes give very good results. 

Shelby Series. — The soils of this series are yellowish gray or 
yellowish brown to brown in color. The subsoils are yellow or red- 
dish yellow or light brown tenacious sandy clays. The subsoils 
are derived from the Kansas drift and occupy steep stream slopes. 
They were originally covered with white oak, some hickor}^, red oak 
and elm. 

Trumbull Series. — The Trumbull series consists of gray sur- 
face soils, underlain by light gray or gray mottled with yellow sub- 
soils, which at an average depth of about 18 inches becomes a mot- 
tled gray and yellow. The soils are without limestone to a depth of 
3 feet. They are derived from shales and sandstones. Corn, oats, 
wheat and hay are the principal crops grown. 

Union Series. — The soils of this series are characteristically 
brown to grayish brown in color, of silty texture and friable struc- 
ture, with j-ellowish brown silty and moderately friable subsoils. It 
is probably partly of loessial origin. The topography is gently roll- 
ing to hilly. 

Volusia Series. — The soils of this series are the result of feeble 
glaciation of the shales and sandstones of the Devonian and the 
Upper Carboniferous rocks of eastern Ohio, southern New York, 
and northern Pennsjdvania. The underlying shales and sandstones 
have given rise to a large proportion of the soil material, which has 
been modified in var}'ing degi'ees by other glacial material. The 
series is well adapted to the production of timothy and small grains. 
Wheat and corn give good yields at lower elevations. Over six 
million acres have been mapped. 

Williams Series. — The soils of this series are of a dark gray to 
brown or dark brown color, generally underlain at 8 to 13 
inches by lighter brown subsoils which grade quickly into 
light gray, ashen or putty colored subsoils of calcareous character 
and usually of fine and often of silty texture. They are derived 
from glacial material and contain gravel and boulders. The sur- 
face is treeless and varies from level prairies to rough hilly terminal, 
morainic belts. Nearly 14,500,000 acres have been mapped. 

Wooster Series. — The Wooster series includes the yellowish 



CLASSIFICATION BY THE BUREAU OF SOILS 89 

brown glacial shale and sandstone soils, having unmottled browTiish 
gray subsoils. When dry the surface in plowed fields is a light gray, 
but underneath the surface or when moist the soils are always 
yellowish or light brown. The subsoils are of a bro^^nish yellow 
with just a. slight tinge of red. They are derived from shales and 
sandstones. Wheat, corn, oats, hay, and potatoes are the principal 
•crops grown.- 

V. GLACIAL LAKE AND RIVEK TERRACE PROVINCE 

The Glacial Lake and Eiver Terrace Province embraces two 
classes of deposits. The first class includes deposits in the basins 
of lakes formed by the advance and retreat of ice during the Glacial 
period. These were temporary lakes which took form during the 
period of the retreat of the ice or lakes that were formed then but 
have since been drained through the operation of natural drainage 
forces. 

The second class of deposits consists of those left within the 
glaciated area by the streams that flowed from the ice during the 
Glacial period. These streams were more abundantly supplied with 
water from the melting ice than at present from the normal rainfall 
of the glacial region. They also carried large quantities of gravel, 
sand and finer material which were deposited in the valleys, form- 
ing new slopes whose grades were determined by the load and cur- 
rent of the streams. Since the reduction of the volumes of the 
streams new valleys have been formed through the old material. 

The province consists of a large number of isolated areas, many 
of them a square mile or less in extent. The river terraces are 
developed as small, irregular areas or strips along the streams. The 
larger areas lie within the former basins of the lakes. The principal 
series are as follows : 

Chenango Series. — This series consists of yellowish to light 
brown surface soils and brown to yellow subsoils. The surface soils 
vary in texture. The subsoils pass into stratified gravel or coarse 
sand at three feet or more in depth. The series includes terrace 
soils occurring along streams. The soils are of high, agricultural 
value, and are well adapted to corn, alfalfa, potatoes, and truck 
crops. 

Clyde Series. — This series is characterized by dark brown to 
black surface soils and gray, drab or mottled gray and yel- 
lowish subsoils derived through deposition or reworking of the soil 



90 SOIL PHYSICS AND MANAGEMENT 

material in glacial lakes or ponds. The soils of this series grade 
into muck and peat. The topography is level and the soil is nat- 
urally poorly drained. They are highly productive and valuable 
for corn, grass, sugar beets, cabbage, and onions. About 1,500,000 
acres have been mapped. 

Dunkirk Series.^ — The soils are derived from the weathering of 
glacial lake deposits and include the lighter colored soils formed 
from such material. The surface soils range from brown to gray 
in color and the subsoils from bro\vn to yellow or gray with or 
without mottling. The topography varies from smooth to rough. 
An area of almost two million acres has been mapped. 

Fargo Series. — This series occurs principally in the old glacial 
Lake Agassiz, in the Eed Eiver Valley, and in other old glacial lake 
beds in the same region. They are very black in color, containing 
a very large per cent of organic matter, in some cases enough to 
make them slightly mucky. The subsoil contains a large amount of 
lime. The topography is level. The area mapped is nearly 3,000,- 
000 acres. • 

Fox Series. — These are gray to brown and of level or slightly 
undulating topography. The material was laid down as outwash 
plains or terraces along streams within the glacial area. 

Manchester Series. — The soils of the Manchester series are 
generally rather sandy in texture and the surface soils are red or 
brown in color. The subsoils are red or reddish and in the lower 
part grade into the glacial till. They are formed from old alluvial 
or lacustrine sediments disposed as terraces in the Connecticut 
Valley. They are adapted to fruit, early truck, grains, and tobacco. 

Merrimac Series. — The surface soils of the Merrimac series 
are broflii to light brown in color and usually underlain by yellowish 
sand and gTavel. They constitute the glacial terraces found along 
nearly all streams in jSTew England. The material consists princi- 
^ pally of crystalline rocks which were ground up by the ice and 
reworked by water. 

Orono Series. — The surface soils are light brown anc^ gray and 
the subsoils are gray. The heavier types occur as estuarine 
and glacial lake plains or outwash plains. The lighter t3^es are 
derived from esker and glacial-delta material. The adaptation to 
crops varies with the texture and drainage. The heavier soils are 
best suited to grass and grains, the intermediate, to general farming, 
and the light sandy ones to truck crops. 

Plainfield Series. — The surface soils of the Plainfield series 



CLASSIFICATION BY THE BUREAU OF SOILS 91 

range in color from brown to grayish yellow, while the subsoils are 
usually* yellow to pale yellow. The series is developed in the deep 
drift-covered areas of Wisconsin, Michigan, and Minnesota, and 
are derived from sandy and gravelly glacial debris washed out from 
the fronts of the glaciers. The type is also found in deep filled-in 
valleys. The greater part of the material of the series has been 
considerably assorted by glacial waters and consists mainly of sand 
and gravel. 

Sioux Series. — This series occurs in the glaciated region of 
the central and northwestern states and comprises the dark brown 
to black terrace soils and with a bed of gravel within three feet of 
the surface. It occurs as narrow areas along streams instead of 
broad outwash plains. 

Superior Series. — The surface soils are gray, brown or reddish, 
with pinkish red to light chocolate red rather dense clay subsoils. 
The series comprises a group of glacial-lake soils developed 
mostly along the margin of Lake Superior. The topography is 
usually level to slightly undulating. The series is well adapted to 
the production of grasses, grains and the general farm crops. 

Vergennes Series. — This series is marked by brown, yellowish 
or gray soils underlain at varying depths by drab to blue or light 
gray clay subsoils, often calcareous. It consists of deep-water sedi- 
ments known as the Champlain clays deposited in post-glacial times 
over glacial drift during a period of submergence. Since the uplift 
these clays have been more or less modified by the stream action 
and colluvial wash from the surrounding highlands. The surface 
is level to gently rolling. 

Waukesha Series.— The Waukesha series is characterized by 
dark brown to black surface soils underlain by yellow subsoils in 
which fine gravel is usually present. They are derived from water- 
assorted glacial debris deposited in broad filled-in valleys or as out- 
wash plains and terraces, and are sandy and gravelly in general 
character. They are more productive than Plainfield soils. 



VI. ATLANTIC AND GULF COASTAL PLAINS PROVINCE 

The Atlantic and Gulf Coastal Plains Province. constitutes one 
of the most important physiographic divisions of the United States. 
This province comprises approximately 365,000 square miles of the 
predominantly flat to smoothly rolling region bordering the Atlantic 
Ocean and extending from the northern end of Long Island in New 



92 SOIL PHYSICS AND MANAGEMENT 

York to the ssoutheni extremity of Florida and along the Gulf of 
Mexico to the mouth of the l\io Grande. There is a broad -gap in 
the Gulf Plain represented by the Mississippi bottoms and the belt 
of loessial soils adjoining the bottoms on the east. 

In its general aspect, the Atlantic and Gulf Coastal Plains 
Province consists of a broad plain which rises gradually either from 
sea level or low bluffs along the coast to the border of the high 
inland regions of ditferent topographic forms. The inner boundary, 
representing the highest part of the main province, varies from 
200 to 500 or 600 feet above sea level. This region, although- 
formerly a plain changing to a gradual slope from the sea inland, 
has been eroded since its uplift above 'sea level to its present vary- 
ing topographic features of low to moderate relief as compared with 
the much more uneven surface of the Appalachian and Piedmont 
regions. The most important series are as follows : 

Acadia Series. — The surface soils are light gTay or white, with 
mottled gray and yellow, or gray, yellow and red friable subsoils, 
carrying lime nodules and iron concretions. They are derived 
mainly from reworked loessial material. The surface is gently, 
rolling, and the series is now timbered with pine, oak, gum, hickory 
and some cypress. It is adapted to the production of corn, cotton, 
peas, and oats. 

Brennan Series. — This series consists of gray calcareous soils 
containing a small amoimt of humus and a large amount of lime. 
They have been derived from Pleistocene deposits in broad valleys. 
They are of higher agricultural value than the former. 

Caddo Series. — The soils are gray to yellow in color. The sub- 
soils are mottled gray and yellow, or gray, yellow and red, and of a 
rather stilf structure. In some places the subsoil has a pronounced 
oravish color, while in others it is a mottled yellow and gray. Low 
sandy mounds or hummocks are a feature of the series. Cotton 
and corn are the principal crops. These soils are most extensively 
developed in northwestern Louisiana and northeastern Texas and 
are derived from reworked loessial material. 

Coxville Series. — The series comprises dark gray to nearly 
black soils derived from the quiet or deep-water deposits of the 
Columbia formation. The subsoils range from a moderately mellow 
friable clay in the upper portion to yello-\Wsh plastic compact clay 
mottled with drab and bright red in the lower portion. The 
topography is prevailingly flat. They are well adapted to cotton, 
corn, oats, and certain varieties of strawberries. 



CLASSIFICATION BY THE BUREAU OF SOILS 93 

Crowley Series. — The soils range from ashy gray to light 
brown in color, with mottled brown, yellow and red, to almost uni- 
formly yellow clay subsoils. Lime and iron concretions are present 
in the subsoil, which is quite impervious to water. This feature 
favors the production of rice. The topography is flat. They are 
typical prairie soils of Louisiana and Arkansas formed or reworked 
loessial material. 

Durant Series. — The series consists of dark gray to dark brown 
surface soils, with yellow to dark brown subsoils. They are derived 
from soft sandstone and calcareous marl. The soils are productive, 
giving fair yields of general farm crops. 

Duval Series. — The soils are marked by their bright red color 
and rather low lime content. They are derived from fluvial de- 
posits of red sands and sandy clays. Three and one-half million 
acres have been mapped. 

Edna Series. — The soils of this series are gray to dark gray. 
The subsoils consist of gray or mottled gray and yellow, heavy, im- 
pervious clay. The topography is level to gently undulating. They 
are derived from the weathering of noncalcareous marine deposits. 
The supjjly of organic matter is low. They are not very productive, 
but cotton, corn and general farm crops are grown to some extent. 
The area mapped comprises 1,500,000 acres. 

Elkton Series. — The soils are light gray to white and the sub- 
soils are mottled whitish gray and yellow. Gravel or coarse sand 
usually saturated with water is found at a depth of 2i/4 to 3 feet. 
They are of rather low agricultural value. 

Goliad Series. — These soils are prevailingly dark gray to black 
with reddish brown to red sandy loam or sandy clay subsoils, in the 
lower portions of which a white, soft, calcareous substratum is en- 
countered. The soil material consists of weathered marine deposits. 
They are fairly productive. 

Greenville Series. — These soils are reddish brown to dark red 
and generally loamy. The subsoils consist of red friable sandy clay. 
The types occupy level to gently rolling areas in the Coastal plains 
uplands. They are well adapted to cotton, corn, forage crops and 
oats. 

Houston Series. — The soils are black and high in lime, espe- 
cially the subsoils, which in some of the types consist of white 
chalky limestone. The members of the series occur principally in 
the black calcareous prairie regions of Alabama, Mississippi and 
Texas. The soils have been derived from the weathering of cal- 



94 SOIL PHYSICS AND MANAGEMENT 

eareoas elays, eluilk beds and rotten limestone, of Cretaceous age. 
The soils of this series are very productive and are devoted chietiy 
to cotton and corn, but alfalfa will grow on some of the types. The 
area mapped comprises 6,300,000 acres. 

Lake Charles Series. — The soils of this series are gray to 
black in color, with mottled yellow and red subsoils carrying lime 
and iron concretions. The surface is marked by low sandy mounds 
or hummocks. The subsoil is quite resistant to the movements of 
moistures, and drainage is poorly established. The soils are best 
suited to sugar cane and gTass. The series occurs on Iwth prairie 
and tree-eovcred areas aiul consists mainly of reworked loossial 
material. The sand mounds are inclined to be drouthy. Some 
rice is grown. 

Leonardtown Series. — The soils of this. series are gray to pale 
yellow in color. The subsoils are mottled gray, yellow and red and 
ordinarily carry clay lenses and pockets of sand. They are gently 
rolling to rolling. They are- best suited to general farm crops. 

Lufkin Series. — The surface soils are light gray and underlain 
by impervious, plastic and gray to mottled gray and yellow sub- 
soils. The difference in texture between the surface soil and sub- 
soil in the case of the sandy members is very marked. The to- 
pography is flat and drainage is poor. The soils are locally known 
as " flatwoods" land. The timber gro^^'th consists largely of scrubby 
oak and post oak. About two million acres have been mapped. 

Maverick Series. — The soils are light gray to brownish in 
color and the subsoils yellowish brown to drab and of heavier tex- 
ture. They are formed by the mixing of limestone and sandstone 
with calcareous clays. 

Monroe Series. — These soils are gray to brown. Avith mottled 
yellow and red friable structure of the subsoils. They occupy nearly 
level to rolling uplands throughout the Atlantic and Gulf Coastal 
Plains and have been derived mainly from the Piedmont- Appa- 
lachian material. The soils are usually deticient in- organic matter. 
They are variously adapted to early, medium and late truck crops. 
The area mapped comprises thirteen and one-half million acres. 

Nueces Series. — The soils and subsoils of this series are gray 
and are undovlaiu by a stratum of stifl*, mottled, grayish clay. The 
soils are derived from wind-blown material originally from the 
residual prairies, which has drifted inland from the coast. The 
surface is prevailing flat, with a few dunes. They are poor agri- 
culturally. The soils are devoted to corn, truck crops, and pasture. 



CLASSIFICATION BY THE BUREAU OF SOILS 95 

Oktibbeha Series. — These soils are prevailingly dull brown 
to j^ellowish brown. The subsoils are composed of somewhat mot- 
tled yellow, gray and red, rather plastic, silty clay. They are under- 
lain by soft rotten limestone. The topography is flat to gently 
sloping. They are locally known as "post oak lands" or "post 
oak prairie lands." When properly handled they produce good 
crops of cotton, corn, Johnson grass, lesjDcdeza, bur clover, and a 
number of other crops. 

Orangeburg Series.- — ^The soils of this series are marked by 
their gray to reddish brown color and open structure. The subsoils 
consist of friable sandy clay. They are confined to the uplands of 
the Atlantic and Gulf Coastal Plains, being most extensively de- 
veloped in a belt extending from southern Korth Carolina to cen- 
tral Texas. This is a very valuable series, its heavier members being 
adapted to corn, cotton, cowpeas, peanuts, potatoes, and cigar leaf 
tobacco. N"early five million acres have been mapped. 

Portsmouth Series. — These soils are dark gray to black and 
are high in organic matter. The siibsoils are light gray to mottled 
gray and yellow and the heavier types are always plastic. These 
soils are developed in flat to slightly depressed, poorly drained situa- 
tions and require drainage before they can be used for agriculture. 
They are adapted to corn, strawberries and truck crops such as 
cabbage, onions and celery. Altogether 2,410,000 acres have been 
mapped. 

Ruston Series. — The soils are gray to grayish bro^vn, and are 
underlain by reddish yellow to yellowish red or dull red moderately 
friable subsoils, prevailingly of sandy clay. They are slightly lower 
in productiveness than Orangeburg. 

San Antonio Series. — These soils are brown to chocolate brown 
in color and have brownish red calcareous subsoils. They are de- 
veloped in the semi-arid regions of southern Texas. They are de- 
rived from calcareous material of sedimentary origin. Under irri- 
gation they give excellent j-ields of a number of crops such as cotton, 
corn, sorghum, vegetables, and alfalfa. 

Sassafras Series. — These soils are distinguished by their yel- 
lowish broAvn to brown color and mellow structure. The subsoils are 
reddish yellow and friable in structure, resting upon beds of gravel 
or sand varying from 214 to 5 feet in thickness. They are developed 
along flat marine or estuarine terraces from 10 to 250 feet ahove 
sea level. They include some of the most productive soils of the 
Atlantic seaboard. Excellent crops of wheat, corn, clover, potatoes, 



96 SOIL PHYSICS AND MANAGEMENT 

melons, berries and vegetables are secured. The area mapped is 
1,717,000 acres. 

Scranton Series. — These soils are dark gray to black, with 
yellow friable subsoils. The topography is flat and the soils are 
generally in need of better drainage. They are well suited to corn, 
oats, forage crops and a number of vegetables. 

Susquehanna Series. — These are gray to reddish gray in color 
and are underlain by mottled red and gray or red, gray and yellow 
plastic heavy clay subsoils. Eed is always the predominating color 
in subsoils, the other colors appearing as mottlings. The soils 
are developed in the higher portions of the Coastal Plain from 
Chesapeake Bay to Central Texas. The heavier members are 
heavy to handle on account of the intractable subsoil. Corn and 
oats are grown extensively in the northern, wtih cotton in southern 
states. More than 2,800,000 acres have been mapped, 

Tifton Series. — The soils are gray to grayish brown in color 
and are underlain by bright yellow, friable, sandy clay subsoils. 
Small iron concretions occur on the surface and throughout the 
soil section. Their presence gives rise to the local name of " pimply 
or pebbly land.'' They are considered very valuable and are adapted 
to cotton, sugar cane, corn, cowpeas, velvet beans, oats, rye, sweet 
and Irish potatoes, pecans, figs, plums, and vegetables. 

Victoria Series. — This series consists of bro^^l to black soils 
with gray to whitish, calcareous subsoils, derived from the Pleisto- 
cene deposits of the Gulf Coastal Plains. The topography is rolling. 
Over four million acres have been mapped. 

Webb Series. — The soils of this series are brown to reddish 
brown with reddish brown to red sul)Soil. They are found in the 
semi-arid areas of the Coastal Plains of Texas. They are culti- 
vated to some extent. ]\Iost types are covered with thick growth of 
mesquite. 

Wilson Series. — The series embraces dark gray to black soils, 
with mottled gray and drab to black subsoils, usually of stiff, 
heavy clay. They are typically developed in the mixed prairie and 
timbered regions of Texas and apparently hold a position inter- 
mediate between Houston and Lufkin series. Eed is practically 
absent. The surface is frequently flat so that water stands after 
heavy rains. The heavier members dry out and bake quickly. Cot- 
ton and corn are the principal crops. 



CLASSIFICATION BY THE BUREAU OF SOILS 97 

VII. RIVER FLOOD PLAINS PROVIlSrCE 

The soils of this province occupy the first bottoms and adjoin- 
ing terraces of streams throughout that section lying east of the 
Great Plains region. Some areas of flood plains soil cover the bot- 
toms and terraces of valleys which have been abandoned by their 
main streams. 

These soils occur in continuous and interrupted strips along 
the banks of streams. They vary from narrow strips a few rods 
wide along the minor drainage courses and those streams which 
pass through gorge-like valleys to broad bottoms several miles in 
width. The broadest strip of strictly alluvial land is along the 
Mississippi Eiver, where, at its confluence with the Arkansas, it is 
75 to 100 miles. 

The soils of this iDrovince include two topographic divisions : 
(1) The first bottoms or present flood plains, and (2) the terraces 
or old flood plains. The material composing these soils is derived 
from very widely distributed sources and from every species of 
rock. The principal series are as follows : 

Bibb Series. — This series is marked by light^colored to white 
compact surface soils and by compact plastic and white or mottled 
white and yellowish subsoils. The material is derived mainly from 
Coastal Plains soils. They are best suited to grass and pastures 
under present conditions. 

Blanco Series. — These have gray to light brown soils and 
brownish subsoils which in the lower portions change to plastic 
heavy materials of a decidedly brown color. The soil and subsoil 
are calcareous. These soils occupy terraces mainly above overflow. 
Soils are well adapted to cotton, corn, Irish potatoes, and alfalfa. 

Cahaba Series. — The surface soils are brown to reddish brown 
and the subsoils are yellowish red to reddish brown. They are ter- 
races principally above overflow. These soils are well suited to cot- 
ton, corn, oats, and forage crops. 

Cameron Series. — These are soils of dark brown to black color 
and tenacious character and highly calcareous subsoil. The series 
occupies broad, shallow basins, occurring typically between river 
channels, and in general is poorly drained. The lower portions re- 
main flooded during the greater part of the year. Alkali is fre- 
quently present in the lower depression. Good crops of corn, sugar 
cane, cotton, and vegeta])les are successfully grown. 

Congaree Series. — The soils and subsoils of this series are 
brown to reddish brown, there being comparatively little change in 
7 



98 SOIL PHYSICS AND MANAGEMENT 

texture, stnicture and color from the surface do\nnvard. They 
occur as lirst bottom of the Piedmont region and in the Coastal 
Plain. Soils are productive, yielding corn, cotton, cane, oats and 
forage crops. 

Frio Series. — Tiiese consist of dark-colored soils which have 
been brought down from the Edwards Plateau and deposited in 
terraces along the larger streams. They are excellent agricul- 
tural soils. 

Genesee Series. — The Genesee series consists of dark brown to 
grayish brown alluvial sediment deposited along the major streams 
and their tributaries throughout the northeastern glaciated region. 
They are subject to overflow. Good soils for corn, oats, sugar beets, 
potatoes, cabbages, and grass. 

Holston Series. — These consist of yellowish bro\TO to brown 
surface soils and yellow subsoils. It is developed in old alluvial 
terraces, sometimes standing '^00 feet or more above the first bot- 
tom of streams. The nuiterial is derived principally from sand- 
stone and shale. The soils give fair to good crops of corn, wheat, 
oats, grass, clover, and forage crops. 

Huntington Series. — These are light brown to brown and the 
subsoils yellow to light brown. Frequently there is little change in 
the color or character of the material. They occur in the limestone 
and Appalachian j\[ountain regions as first bottoms. They are ex- 
cellent soils and well adapted to corn, oats, grass and forage crops 
under proper climatic conditions. More than 1, '337,000 acres have 
been mapped. 

Kalmia Series. — The surface soils are gray to gTayish yellow. 
The subsoils are mottled gray and yellow. The series is found along 
streams of the Coastal Plain on terraces above overflow. The sur- 
face is flat. When properly drained the soils are suited to corn, 
cotton, sugar cane, and forage crops. 

Laredo Series. — This series consists of gray to light brown, 
calcareous soils with gray, calcareous subsoils. They occur as ter- 
races along streams in south Texas, and are quit-e valuable when 
irrigated. 

Lintonia Series. — The surface soils of this series are light 
brown or yellowish brown and of silty texture. The subsoils are of 
slightly lighter color. They occupy stream terraces and alluvial 
land. Grass, forage crops, corn, oats, Irish potatoes, peanuts, cab- 
bage, and vegetables are grown. 

Miller Series. — These soils are of chocolate brown to pinkish 



CLASSIFICATION BY THE BUREAU OF SOILS 99 

red color, with chocolate red or pinkish red subsoils. Both strata 
are calcareous. They are first bottom soils in Texas and are well 
adapted to cotton, corn, alfalfa, forage crops, and cabbage. 

Myatt Series. — The Myatt soils are gray to dark gray. The 
subsoils are of gray to mottled gray and yellow color and impervious 
character. They represent the poorest drained portion of the 
Coastal Plain stream terraces. They lie principally above overflow. 
When drained they may be used quite profitably for sugar cane, 
corn, and a number of forage crops. 

Ocklocknee Series. — These soils are dark gray to brownish, 
with brownish or mottled brownish, j^ellowish and gray subsoils. 
They occur in the Coastal Plains and are subject to overflow. Corn, 
oats, and forage crops are grown. 

Osage Series. — They consist of dark gray to almost black 
alluvial wash from the sandstone and shale soils of the prairie 
regions. They produce good yields of general farm crops. 

Podunk Series. — These are dark brown in color and overlie 
lighter brown to brownish gray or yellowish gray subsoils. They 
occur as rather high bottom lands, but are subject to overflow. 
They produce grass and heavy truck crops well. 

Sarpy Series. — These soils range from light gray to nearly 
black. They possess loose silty or fine sandy subsoils distinctly 
lighter than the surface. They occur in the bottoms of the Missis- 
sippi and Missouri rivers and their large tributaries. They are very 
productive and adapted to grains, grasses, and alfalfa. 

Sharkey Series. — These soils are of yellowish brown to drab 
color, with mottled rusty brown, bluish, drab and yellowish sub- 
soils, of very plastic structure. They are very heavy alluvial soils of 
the Mississippi river, commonly called " buckshot land." They are 
well adapted to corn, sugar cane and cotton. About 1,600,000 acres 
have been mapped. 

Trinity Series. — These soils are dark brown to black first bot- 
tom lands mainly derived from the Huston series. The organic 
matter content is high and lime is usually present. They occur 
as flat lands in shallow valleys. Large crops of alfalfa, cotton and 
corn are produced when the soil is well drained. The area mapped 
comprises 1,280,000 acres. 

Uvalde Series. — These soils are alluvial and occupy broad level 
flood plains in Texas. They are light in color and very floury to 
the feel. 

Wabash Series. — The soils are of a dark brown to black color 



100 SOIL PHYSICS AND MANAGEMENT 

ami hig-h in ori^-aiiii.' inattor. The subsoils are liuhtor drab or gray. 
Tlioy oi'c'ur as tirst bottoms aloiii^- the JMississippi. They grow 
large crops o( i;rass ami eorii. One luilliou nine hundred acres have 
been mapped. 

Waverly Series. — The soils are light gray in color and overlie 
gray or mottled yellowish and grayish subsoils. They occur as first 
bottom laud along streams issuing from the loessial region of the cen- 
tral }u'airie states. They are fairly well adapted to corn and grass. 

Wheeling Series. — These soils are brown to yellowish brown 
and are underlain by gravel usually within o feet of the surface. 
They occupy the gravel terraces along the streams that flowed from 
the iee-covered regions. 

Yazoo Series. — The color of the surface soil ranges from gray 
slightlv darkened with organic matter to light brown, while the 
subsoils are of mottled grayish, rusty brown and sometimes bluish. 
They occur in the flood plains of the Mississippi river. They are 
well suited to cabbage, onions, peas, lettuce, Irish ai\d sweet po- 
tatoes, cucumbers, melons, etc. Cotton, corn, and forage crops give 
good results on the heavy types. 

Ylll. OKKAT PLAINS REGION 

The Great Plains K'egion is bounded on the north and east by 
the tilacial and Loessial province, on the east and southeast by the 
Limestone Valley and Uplands province and the Gulf Coastal 
riains, and on the west by the l^ocky Mount^vins. It has a maximum 
width of GOO miles. In altitude it varies from 1000 to 6000 feet 
above sea level, \\here not eroded it is a level or gently sloping 
plain. There are areas of exeessively eroded or " bad land " to- 
pography. The Creat Plains region extends from the Eio Grande to 
Canada. The Upland soils are divided into the following as to 
origin : 

(1) Residual Material. — The residual soils are of widespread 
occurrence and constitute the most extensively developed and im- 
portant province. Owing to their Avide distribution these soils are 
subject to a wide variation of climatic influences that have been 
important t'actors in their formation. The series are as follows: 

Bates Series. — These are of dark gray color, while the subsoils 
are yellowish and mottled red or yellowish or bufp in the npper part 
and mottled with yellow and red in the deeper sections. They are 
treeless and of undulating topography. The cjops are cliiefly com, 
wheat, flax, and oats. 



CLASSIFICATION BY THE BUREAU OF SOILS 101 

Benton Series. — 'J'lie soils are light brown or grayish brown to 
gray colored, with light gray subsoils. They are derived from lime- 
stone and shalo and mostly used for grazing. 

Boone Series. — 'I'his series consists of light gray soils of low 
organ ic-nuitter content underlain by pale yellowish to slightly red- 
dish yellow and often mottled, porous subsoils. They are derived 
from sandstone and shales. The soils are often timbered and are 
frequently thin and unproductive. The principal crops are corn, 
oats, wheat, and hay. 

Clark Series. — This series includes dark gray to brown or black 
scm'Is and gi'ayish calcareous subsoils. They produce fair crops of 
coi'ii, kallr. wheat, sorghum, and alfalfa. 

Crawford Series. — Thei^e comprise residuaV limestone soils of 
dark brown to reddish brown surface soils and reddish brown to 
red subsoils. Cotton, corn, wheat, oats, alfalfa, clover, and timothy 
arc grown. 

Englewood Series. — The soils are of brown to reddish brown 
color. The subsoils are usually reddish brown but sometimes brown. 
They are derived from shale and sandstone. They are generally 
adapted to corn, kafir, sorghum, and hay. 

Epping Series.— The soils are white or light gray to buff and 
are underlain by subsoils of similar character. They are derived 
from shales and indurated clays. Wheat, barley, potatoes, and 
alfalfa are the principal crops. 

Morton Series. — The soils are brown in color and contain a 
high content of organic matter. The subsoils are light brown to 
gray and are rich in lime. They are derived from sandstone and 
shales. Wheat, barley, and flax are the principal products. More 
than 13.000.000 acres have been mapped. 

Oswego Series. — The soils are light gray to dark gray» while 
the subsoils are drab to yellow and are compact and impervious. 
They are derived from shale and sandstone. Wheat, corn, oats, flax, 
rye, and potatoes are grown. 

Pierre Series. — The soils of this series are light brown to dark 
browai, the innnediate surface often being light gray. They are 
usually compact and refractory. The subsoils are brown and com- 
pact and grade into a substratum, of partially weathered shale. The 
surface is generally irregular, being dissected or eroded and marked 
by hills and ridges. Drainage is generally good. The types fre- 
quently contain rather excessive amounts of alkali. 

Sidney Series. — The soils consist of brown surface soils, with 



102 SOIL PHYSICS AND MANAGEMENT 

light gray to white, calcareous, lloiiry, silty clay subsoils. They are 
derived from calcareous conglomerate. The more loamy types are 
good for general t'aru\iug. 

Summit Series. — The soils are dark gray to black, with m.ot- 
tled yellow and gray subsoils. They occupy nearly flat to sharply 
rolling prairies and are derived from calcareous shales. Corn, 
wheat, oats, timothy, clover, and alfalfa are the principal products. 

Vernon Series. — The soils are reddish brown to red. The 
subsoils are usually red but sometimes reddish brown or brown in 
the upper part. Corn, wheat, oats, cotton, kahr and sorghum are 
the chief products. They are derived from sandstones and shales. 

(2) Glacial Material. — The soils derived from this material 
do not occur extensively in this region. They are represented 
by a single series, the O'Neill. The soils are dark gray to 
brown, underhiin by light brown subsoils resting upon sand or 
gravel. The to]iography varies from nearly level to rough and 
broken. The series is derived from ghicial drift which underlies the 
loess. The deeper members have a high value for small grains, corn, 
potatoes, and forage crops. 

(,'0 Alluvial Fan and Valley-Filling Material. — These have 
of only local occurrence. They are represented by three series of 
small extent. 

(4) Wind-laid Material. — This series occupies a very exten- 
sive area in Kansas, Nebraska and South Dakota. The principal 
series are the Canyon, Colby, and Valentine. 

Canyon Series. — These soils are light brown or ashy brown 
and the subsoils are yellowish gray. They are mainly derived from 
loessial material and are adapted to grazing and locally to com, 
milo, katlr, and sorglnnn. The series occurs in Kansas and 
Nebraska. 

Colby Series. — The soils are ashy gray or brownish gray. The 
upper subsoil is similar to or lighter in color. They are derived 
from loessial deposits. Wheat, corn, and forage crops are grown. 

Valentine Series. — The soils consist of brown to dark brown, 
with light brown to brown and usually heavy subsoils. They are 
adapted to corn, potatoes, truck, and hay crops. 

(5) Alluvial Fan and Valley Filling Material. — These have 
been derived from the great areas of Tertiary deposits with those 
less extensive areas of local alluvial fan and colluvial material. 



CLASSIFICATION BY THE BUREAU OF SOILS 103 

They are unconsolidated, but include certain zones of material 
which is calcareous and more or less indurated or cemented. 

Amarillo Series. — These include chocolate brown to reddish 
brown soils, with brown to reddish brown subsoils. The subsoil 
grades into a white or pinkish white calcareous material within 
three feet of the surface. They are derived from sandstone, shale, 
limestone, and crystalline rock. More than eleven million acres 
have been mapped. 

Colorado Series. — The soils are of gray to reddish brown color 
and contain fine quartz and feldspar fragments. The subsoils are 
reddish brown. They grow vegetables, tree fruits, alfalfa, and 
melons. 

Dawes Series. — The soils are ashy gray to light brown in color, 
with white to pinkish white subsoils. 

Gannett Series. — The soils are light brown, with yellowish 
sand to light sandy loam subsoils. They are mostly utilized for 
pasture. 

Greensburg Series. — The soils are brown to dark brown in 
color and the subsoils brown to yellowish brown. The soils are 
derived mainly from Plains Marl. They are usually treeless and 
produce wheat, corn, kafir, and sorghum. 

Pratt Series. — The soils are brown, with dark reddish brown 
rather compact sticky subsoils, usually loam to clay loam in tex- 
ture. They retain water well and under favorable conditions the 
soils are quite productive, giving good yields of kafir, corn, sorghum, 
and wheat. Nearly 2,000,000 acres have been mapped. 

Richfield Series. — The soils are grayish brown, with grayish 
brown calcareous subsoils. They are retentive of moisture and 
produce wheat, corn, alfalfa, and forage crops. More than 8,000,000 
acres have been mapped. 

Rosebud Series. — The surface soils are dark gray to brown. 
The subsoils are light colored, almost white, and very calcareous. 
The topography ranges from undulating to steeply rolling and 
where badly eroded constitutes " bad land." More than 5,000,000 
acres have been mapped. 

Zapata Series. — The soils have gray calcareous surface, with 
subsoils of similar color and texture. They have a very low value 
for agriculture. They are used for grazing. 

(6) River Flood Plain Material. — These soils are the flood 
plains and terraces along streams. They occur widely scattered 



104 SOIL PHYSICS AND MANAGEMENT 

over the region, but are especially well developed as the wide 
valleys along the larger streams. The series are as follows : 

Arkansas Series. — This series includes grayish brown or dark 
brown soils, with yellowish brown subsoils resting upon gravels and 
sands. The substratum is sometimes so near the surface as to 
cause deficiency of moisture. Soils may be subject to overflow. 
Wheat, corn, forage crops, and alfalfa are the principal 'crops. 

Cheyenne Series. — The soils are brown with lighter brown or 
yellow subsoils underlain by sands and gravels. The soils occupy 
high valley terraces laid down while the streams were choked with 
ice. They are productive and adapted to -grazing, small grains, 
corn, and potatoes. Under irrigation they grow alfalfa and fruits. 

Laurel Series. — The soils are dark gray to brown and the sub- 
soils are usually lighter in color and are underlain by porous gravel. 
Corn, small grains, forage, melons and cantaloupes are grown. 

Lincoln Series. — The soils are dark brown to dark gray or 
nearly black, while the subsoils are dark gray to brawn. Corn, 
forage crops, small grains, and alfalfa are grown. More than 
2,300,000 acres have been mapped. 

Tripp Series. — The soils are brown to light gray, while the 
subsoils are light gray to white. They are of alluvial origin. They 
are adapted to corn, wheat, oats, potatoes, and vegetables. 

Wade Series. — The soils are brown to dark gray, drab or dark 
brown, while the subsoils are light brown, brown or gray to dark 
drab, rather heavy and compact. The crops are corn, small grain, 
flax, potatoes, and alfalfa. 

IX. ROCKY MOUNTAIN AND PLATEAU REGION 

This region covers the areas of elevated mountains and plateaus 
extending from Canada southward to the lower lying, arid, treeless 
plains and isolated ranges of the arid region of Arizona and New 
Mexico. 

The soils vary widely in character owing to the great variety 
of material from which they are derived and the number of agencies 
active in their formation. Weathering in places has given rise to ex- 
tensive areas of residual soils, while at the bases of the mountains 
large areas of colluvial soils are found. The stream valleys have 
terraces and flood plains, while the broad intermountain basins 
have extensive deposits of sediments. 

(a) Uplands. — San Luis Series. — The soils are reddish 
brown in color and porous in structure and are underlain by sands 



CLASSIFICATION BY THE BUREAU OF SOILS 105 

and coarse rounded gravel. They are derived mainly from vol- 
canic rock. 

(b) River Flood Plains. — Billings Series. — The soils are gray 
to drab, with the subsoils similar in color, structure and texture. 
They are derived mainly from shales and sandstones, and axe adapted 
to a wide range of crops under favorable conditions of irrigation. 

Laramie Series. — These soils are light brown to. grayish brown 
with a slight reddish cast. The subsoils are lighter gray or more 
reddish, sometimes becoming yellowish gray, and are underlain by 
sand or sandy loam with gravel. They are treeless plains. 

Mesa Series. — The soils are pinkish red or reddish gray to 
light reddish brown. The subsoils are of lighter reddish gray or 
gray color and heavier texture. Where irrigated, fruits, alfalfa, 
and general farm crops do well. 

X. NORTPIWESTERN" IXTEEMOUNTAIN' REGION 

This region lies between the Pacific Coast region on the west, 
the Eocky Mountain region on the north and east, and the Great 
Basin region on the south. 

The rocks of this region are mostly effusive or volcanic and the 
soil material is derived largely from these, either by weathering of 
solid material or from fragments ejected from volcanoes. 

(a) Uplands. — Ephrata Series. — These soils are of light gray- 
ish brown to yellowish brown color, while the subsoils are porous but 
compact. They consist largely of glacial subangular or rounded 
gravel or boulders. 

Quincy Series. — The soils are grayish brown and usually of 
loose porous structure. The subsoils are similar in color and tex- 
ture but slightly more compact. They are wind-laid material. 

Walla Walla Series. — This series consists of sticky, brown to 
dark brown soils about three feet deep underlain by yellow silt loam 
subsoils which are often sticky and plastic. The topography is high 
rolling hills. The soil material is wind-laid. Wheat, barley, and 
oats are the principal crops. 

Winchester Series. — The soils and subsoils of this series are 
dark gray to nearly black and consist mainly of dark-colored angular 
fragments of basalt. The fine material is wind-laid. 

(b) River Flood Plains. — Boise Series. — Soils are of light 
gray to light brown color. The subsoils are similar to the soils in 
color. They, are underlain by a calcareous hardpan stratum. They 
are of alluvial orisrin. 



106 !:?01L rHYSlCS AND MANAGEMENT 

Caldwell Series.- — 'Vh'o soils nuiiiv in oolor from irniy to dark 
t^ray or Uhuk. 'I'lio subsoils arc usually of soniowhat liijhlor shailo, 
\aryini;- from liuiit uray to drab, and are uiulorlaiii by gravel. 
Sinnll ui'ains. liiuothy aiul otlun- grasses, alfall'a, potatoes, and 
sugar heels are gri>\vii. 

Yakima Series.- The soils range from light to grayish brown 
\o yt^low ish hrcnvn ov light brown in eolor. 'They are usually tree- 
less plains and o( alius lal origui. The imnunliate surface material 
is derned from basalt ie or other eruptive roeks. 

XI. iiKi'.vr nAsiN mxaox 

This region embraees praetieally all o( the (.ireat Basin of In- 
terior Hrainage. It inelmies all ot' JSovada with the exeeptioii of 
the e\iren\e southeastern part>, the -western part of Utali, a small 
part o( southwestern Idaho, the south eenrral part of Oregon, and 
the greater part of the eastern margin of California, 

The region is eharaeterized by numerous isolated ridges and 
mountain ranges running in a general north and south direetiou, 
arid treeless plaii\s and intermittent streams which disappear in the 
gra\elly or sandy soil or discharge into broad lake basins mostly 
without outlets. Many of these basins were lakes in (Quaternary time. 

The soils are elassitied according to the agencies contributing 
to their formation, 

(a") Uplands. — Bingham Series. — This series occupies the 
lower mountain and upper valley slopes and valley terraces or plains 
and is foruu\l from moui\tain wash and delta coi\e dei>osits. They 
arc quite fertile when irrigated and are adapted to alfalfa, grains, 
sugar beets, vegetables, and fruits. 

(^10 River Flood Plains. — Jordan Series. — The soils are 
usually dark in color but sometimes light gray or reddish, the. 
heavier lower lying members being underlain by gray, black, yellow 
or red contpact heavy and often calcareous subsoils. They are de- 
voted to grains, alfalfa, fruits, and truck crops. 

xii. .\iur» soirinvKsr kkoiox 

This region tx>Yei"s the southwestern third of Arizona, a large 
area in south central New Mexico and in norThwesteri\ Texas. It 
inehides also a small area in southeastern Nevada and the soiith- 
oastern extremity of California. 

The region consists of sandy, gravelly sloping or tlat treeless 
plains from which rise frei]uent low roun.dcxi lulls aiul occasional 



CLASSIFICATION BY THE BUREAU OF SOILS 107 

flat topped mesas and many isolated, elongated mountain ridges. 

(a) Uplands. — Glendale Series. — These soils range from light 
gray or grayish brown to dark brown or chocolate in color and are 
underlain by gray to light brown highly calcareous subsoils. When 
irrigated they produce alfalfa, forage crops, vegetables, grapes and 
citrous fruits. 

Imperial Series. — The soils are generally of light or reddish 
color, the heavier members being compact and plastic, poorly 
drained and alkaline. The soil material represents old lake deposits 
derived mainly from sandstone and shales. 

Indio Series. — The soils are light gray to slate colored, porous, 
and underlain by coarser sand. They are derived from granites 
mixed with shales and sandstones. Melons, sweet potatoes, truck 
crops, etc., are grown under irrigation. 

Yuma Series. — 'I'hese soils are usually rather compact. The 
subsoil is similar to the soil except that at a depth of 2 to 6 feet 
layers occur that have the particles slightly cemented together with 
calcium carbonate. They generally occupy mesh lands. They are 
adapted to citrous fruits, figs, grapes, and vegetables. 

(b) River Flood Plains. — Gila Series. — The soils of the 
lighter types are prevailingly of light yellowish brown, light grayish 
brown or slightly reddish brown color and porous structure. The 
heavier types range in color from brown or chocolate brown to dark 
gray or black and are compact. The series occupies stream flood 
plains and second bottoms or recent terraces. 

XIII. PACIFIC COAST REGION 

This region includes the area of California, Oregon and Wash- 
ington west of the Cascade, Sierra Nevada, Sierra Madre and San 
Jacinto Mountains. A broad valley extends almost the entire 
length with only slight interruptions, 

(a) Upland. — Altamont Series. — Soils are light brown to dark 
brown in color with a reddish tinge when wet. Subsoil is heavy, 
rather compact reddish brown or light brown clay loam or clay. 
The series occupies hilly to mountainous regions. The members 
of this series are residual, being derived from sandstone and shales. 
Hay and fruits are grown. 

Corning Series.— The soils are of reddish brown or red to deep 
red color, rather sliallow, easily puddled, and hard to handle except 
under proper moisture conditions. The subsoils are reddish brown 
to deep red, of heavy and compact structure and impervious to 
moisture. The soils occupy sloping to undulating and liilly and 



108 SOIL PHYSICS AND MANAGEMENT 

dissected upland terraces and valley plains. They are poorly 
adapted to general farming. 

Everett Series. — These soils range from light brown to light 
reddish brown in color and are of silky texture and porous structure. 
Large amounts of organic matter often occur in the immediate sur- 
face. The subsoils are light l)rown to gray and usually gravelly and 
porous. The material is of glacial origin and is derived from 
basaltic and intrusive rocks. Heavy forests abound. Some of the 
less porous types are adapted to dairying, orchard, and small fruits. 

Fresno Series. — The soils vary in color from gray to light ash 
broM'n, the- heavier low-lying members sometimes assuming a dark 
gray color as a result of accumulations, of organic matter. They 
are usually free from gra,vel; a layer of white or bluish gray, im- 
pervious, calcareous, alkali-carbonate hardpan varying in thickness 
from a fraction of an inch to, several inches separates the soil and 
subsoil. The hardpan slowly softens under irrigation, but is nor- 
mally impenetrable to the roots of growing plants. They occur as 
old alluvial or colluvial deposits derived from granite rocks. If 
the hardpan is not too near the surface and irrigation is practiced 
alfalfa, grapes, fruits, and vegetables do well. 

Hanford Series. — The soils are generally of light grayish 
brown or buff to light brown color, the heavier members carrying 
considerable organic matter and becoming dark gray to nearly black 
when wet. They are micaceous, smooth to the touch, friable, and 
of porous structure, generally free from gravel or boulders. The 
soil material re^Dresents recent alluvial stream deposits derived 
mainly from granite rocks. When irrigated they are well adapted to 
tree fruits, raisin and table grapes, nuts, vegetables and truck crops. 

Hesson Series. — The soils are dark reddish brown and under- 
lain by yellowish brown to reddish brown subsoils of compact struc- 
ture. Bounded gravel and small boulders are common on the sur- 
face. The series occupies eroded terraces of undulating to rolling 
topography, usually several hundred feet above the valley bottoms. 
The material has been derived mainly from basaltic rocks and con- 
sists of old alluvial or marine terrace deposits. They are well 
adapted to general farming and orchard fruits. 

Melbourne Series. — These soils are light brown to reddish 
brown in color and often dark brown in the immediate surface. 
When wet they are sticky and untractable, but under favorable 
moisture conditions are easily tilled. They are derived princi- 
pally from shales and sandstones. The topography varies from 



CLASSIFICATION BY THE BUREAU OF SOILS 109 

rolling to hilly. Much is too rough for the Use of farm machinery. 

Maracopa Series, — ^The soils range from dark gray through 
the darker shades of brown and chocolate to black. They are loose, 
porous, ordinarily well drained and free from alkali. The soils 
represent assorted, colluvial material, largely derived from granite 
rocks. ^^Hien water is supplied they are well adapted to fruits, 
vines and general farm crops. 

Lynden Series. — The soils are light brown to reddish brown 
and in the lighter textured sandy types often light gray on the 
surface. The subsoil is sandy or gravelly. Drainage is usually ex- 
cessive. The soils are derived principally from stratified deposits 
of sand and gravel formed by glacial outwash. They occupy gently 
rolling upland terraces and plains formerly glacial flood plains, 
now dissected and eroded. All types are suited to agriculture. 

Olympic Series, — These soils are. light brown and brown with 
a reddish cast. The subsoils are generally of compact structure and 
somewhat lighter in color than the soils. They are derived mainly 
from basaltic rock. The topography is rough to mountainous. 
Rainfall is abundant and the soils are heavily forested. When not 
too rough they may be used for general farming and dairying. 

Oxnard Series. — The soils are generally of dark color and 
compact structure, and though sometimes underlain by porous 
subsoils of light texture, are generally underlain by heavier sub- . 
soils. The subsoils lack the red color and adobe structure of the sub- 
soils of the Placentia series. They represent alluvial delta plain 
deposits. These are particularly adapted to the production of lima 
beans. Sugar beets, barley, and vegetables do well. 

Placentia Series. — The soils are reddish bro^vn or brown and 
underlain by heavy, compact, red loams or clay loams of tough, 
impervious adobe structure. The soil material consists of alluvial 
outwash, deposits of intermittent or torrential mountain streams. 
They are derived from granitic rocks. They are tilled with diffi- 
culty but retain moisture well and produce grains, citrous fruits, 
, and beans. 

San Joaquin Series. — The soils are prevailingly red and fre- 
quently gravelly. Both the finer soil particles and gravel are 
rounded. The soils are underlain at depths ranging from 2 to 
3 feet by red or mottled indurated clay or sandy layers and some- 
times by gravel and cobbles cemented by iron salts into a dense, 
impenetrable hardpan. Some of the members are used in the 



110 SOIL PHYSICS AND MANAGEMENT 

proiliu'tion of citrous and t^louc I'ruits. iiixs, grapes, small fnii^ 
and triu'k crops. 

Stockton Series. — Tho lighter luoiubors of this series have a 
InitV to reddish or ehooohito brown color. The heavier members 
generally exiiibit a marked adobe structure, are usually free from 
gravel, and range from dark browu to dark gray or black in color. 
The heavier members are devoted nuiinly to the production of 
grains and hay. 

Redding Series. — The soils range from reddish gray to deep 
red. are usually gravelly and sometimes carry large amounts of 
alkali and partially indurated clay-iron hardpan. Strawberries 
and bramble fruits yield abundantly. 

Whatcom Series. — The soils of the Whatcom series are of a 
deep reddish brown color and prevailingly of tine texture and rather 
eompaet structure. " The surface soil is often dark brown or nearly 
black. Subsoils consist of drab to gray plastic and compact heavy 
silts, the upper portion carrying some gravel and glacial boulders. 
Soils are derived from compact glacial drift and occupy areas of 
undulating to rolling upland. The soils are adapted to small and 
orchard fruits, potatoes, vegetables and hay crops. 

Willows Series. — The soils range in color from bro\m to red- 
dish brown or dark chocolate brown and are free from gravel. 
The subsoils are light brown to reddish brown or sometimes yel- 
lowish aj\d mottled with gray. They have a compact, relatively 
impervious structure and often contain lime and gypsum. They 
are derived mainly from calcareous shales, sandstone, and shaly 
sandstone rocks. Where well di-ained and free from alkali, they are 
well adapted to the production of alfalfa, grains and. with the ex- 
ception of those areas of extremely heavy texture, sugar beets. 

Yolo Series. — This series embraces alluvial soils of brown or 
dark brown color, underlain by lighter brown subsoils. The types 
have been derived from schists and other metamorphic rocks, with 
some material from shaly sandstones and shales. Where capable 
of irrigation, fruits, vegetables, and forage crops can be grown. 

(b) River Flood Plains — Chehalis Series. — The soils are of 
recent alluvial origin, occupying stream valleys. travei"sing the 
region of residual basaltic soils that vary from gray or drab to 
reddish browm. some of the heavier types containing very much 
orgiinic matter and showing a dark bn>wn to black color. The sub- 
soils vary from yellow, gray or mottled to light brown, dark brown, 



CLASSIFICATION BY THE BUREAU OF SOILS 111 

or reddish l)rovvn to black in color. These soils are very productive. 

Puget Series. — The soils are brown to grayish brown or drab 
and J'roquently mottled with iron stains. The heavier members are 
of rather compact and tenacious structure, containing a large 
amount of organic matter, and are usually friable under cultiva- 
tion. The subsoils are light brown to drab or gray marked with 
iron stains. They occupy flood plains in the vicinity of estuaries 
or stream outlets. They are very productive and are classed among 
the very best soils of the region. Oats, forage, hay and truck crops 
and fruits all do well. 

Sacramento Series. — I'he soils are dark gray, drab or black, 
often contain large quantities of organic matter and are six feet 
or more in depth. The series occupies stream bottoms and river 
flood plains. Alkali salts are sometimes encountered. Where pro- 
tected by levees, the soils are productive and adapted to the inten- 
sive production of sugar beets, truck crops, beans, hops, potatoes, 
alfalfa, and prunes, pears and other fruits. 

Salem Series. — The soils are dark brown to black in color and 
underlain by compact reddish yellow subsoils or by sands and 
gravels. They are recent alluvial deposits derived from basaltic 
rocks. Grains, truck crops and hops are the principal crops. 

QUESTIONS 

1. Wliat is a soil Region? A Province? 

2. How many of eacli? 

3. Define a soil series. 

4. Define a soil class. 

5. What is a soil type? 

(). Where does the Cecil series occur? 

7. What are its cliaracteristics? 

8. What are the characteristics of the De Kalb series? 

9. Give characteristics of Clarksville series. 

10. Give characteristics of Carrington series. 

11. Give characteristics of De Kalb series. 

12. Give characteristics of Marshall series. 

13. Give characteristics of Miami series. 

14. Give characteristics of Volusia series. 
l.T. (live characteristics of W'illiams series. 
16. Give characteristics of Norfolk series. 

17'. (xive characteristics of Orangeburg series. 

18. Where is the Great Plains region? Give two series. 

10. Where is the Arid Southwest region? 

20. Locate the Piedmont Plateau Province. 

21. Locate the Appalachian Mountain and Plateau Province. What are 

the two principal series ? 

REFERENCE 
Marbut, C. F., Bennett. H. H., Lapham, J. E., and Lapham, M. H., Bulletin 
96, Bureau of Soils U. S. D. A, 



CHAPTER IX 

SUB-PROVINCES, CLASSES, TYPES AND SURVEYS 

In working out the classification of soils in detail in a single 
state^ it may be necessar}' to make other divisions, or sub-provinces, 
the soils of which have a common origin, but differ from those of 
other sub-provinces in some fundamental characteristics. 

Sub-provinces. — On this basis the glacial and loessial province 
of Illinois has been divided into the following sub-provinces: 
(1) Unglaciated, comprising three areas, the largest being in the 
south end of the state; (2) Illinoisan Moraines, including the 
moraines of the Illinoisan Glaciation ; ( 3 ) Lower Illinoisan Glacia- 
tion, covering the south third of the state; (-1) Middle Illinoisan; 
(5) Upper Illinoisan; (6) Pre-Iowan, but now believed to be part 
of the Upper Illinoisan; (T) lowan Glaciation; (8) Deep Loess 
Area, including a zone a few miles wide along the AYabash, Illinois 
and Mississippi rivers; (9) Early Wisconsin Moraines; (10) Late 
Wisconsin Moraines; (11) Early Wisconsin Glaciation ; (12) Late 
Wisconsin Glaciation; (13) Old River Bottom and Swamp Lands, 
found in the older or Illinois Glaciation; (1-1) Sand, Late Swamp 
and Bottom Lands, those of the Wisconsin and lowan Glaciation; 
(15) Gravel Terraces formed by overloaded streams draining from 
the glaciers and gravel outwash plains; (IG) Lacustrine Deposits, 
formed by Lake Chicago or the enlarged Lake ]\Lchigan. 

Soil Classes. — The soils of these sub-provinces are divided 
into classes based primarilv on texture. The classes are as follows: 

(1) Peats, (2) Peaty Loams, (3) Mucks, (-t) Clays, (5) Clay 
loams, (6) Silt loams, (7) Loams, (8) Fine sandy loams, (9) 
Sandy loams, (10) Sands, (11) Gravelly loams, (12) Gravels, (13) 
Stony loams. These are further divided into soil types. 

Soil Types. — A soil type is the unit of soil classification. It 
is a soil unit which throughout the area has the same physical, 
chemical and biological characteristics. Li the establishment of 
soil types, the following factors are taken into account: (1) Origrin, 
whether residual, cumulose. colluvial, sedimental, glacial or eolial. 

(2) The topography or lay of the land. (3) The native vegfetation, 
as forest or prairie. (4) The strata or character of surface, sub- 
surface or subsoil. (5) Physical composition or texture of the 

112 



SUB-PROVINCES, CLASSES, TYPES AND SURVEYS 113 

diU'creiit strata. ((i) 'I'he structure or gramilutioii. (7) The 
color of tlie strata. (H) 'I'lie natural (Iraiiiage. (U) The amount 
ol; organic matter present. (JO) The agricultural value, based 
upon its natural j)i-o(luctiveness. (11) The ultimate chemical com- 
])osition and I'cactioii, wlietli(!r acid, neutral or alkaline. 

Naming of Soil Types. — At first thought it might seem a very 
easy and simple matter to name soil types. It is on a single farm, 
hut the dilliculty increas(!S witli the size; of the area, the number of 
diH'ererit soils, and the; dclail dcsiftMl. I^'rom tin; standpoint of 
everyone cf^nccrned, hut m<jre esjjccially fnjju that of the farmer, 
the simpler and more expressive the name the better, and the easier 
it will be to associate it with the soil. To a certain extent the name 
should be descrif)tive of the type. According to the nomenclature in 
use by tho Hur(;ari of Soils, names of soil types usually consist of 
two parts, the series name and the cljiss name, with sometimes a 
modifying word included. '^J'he series name is that of some locality 
where the soil in question was first found or where it is well de- 
veloped. This gives names as follows: Cecil silt loam, Marshall 
fine sand, Marshall black clay loam, etc. 

The above system of naming is applical)le to extensive areas, 
but for a limited area, su(;h as a single state;, a more expressive 
system may lie devised. After the texture, one of the most striking 
characteristics of soils is the color. In the Jiaming of soils in 
Illinois, a combination of color and texture together with other 
descriptive terms, when necessary, has been adopted as conveying 
the most meaning to those who use the name. Without ever having 
seen it, the name, so constructed, gives a very good idea of the 
character of tlu; soil. As illustrations, gray silt loam on tight clay, 
yellow silt loam, brown silt loam on gravel, and medium peat on 
rock may he given. 

There are such great variations in color that these color dis- 
tinctions do not always strictly apply. The soil on rolling and hilly 
land is usually of a yellow color either on the surface or immediately 
beneath the surface sfu'l, so that these are called yellow silt loams, 
yellow fine sandy loams, etc. The undulating timber soils are yellow 
or grayish and the term or name yellow-gray is applied to them. 
Prairies are either dark gray, brown, or black. The use of the 
term "on" as part of a soil type name indicates the presence of cer- 
tain substrata within 30 inches of the surface. Tf the term "over" 
is used, the material, such as sand, gravel, or rock, is more than 30 
inches below the surface. 
8 



114 SOIL PHYSICS AND MANAGEMENT 

Classes, Types and Phases in Illinois. — It may be of interest 
to give the classes of soils and their limits, with some of the types 
and their phases as used in the Illinois classification. In numbering 
soir types a system somewhat similar to the Dewey library system 
has been used, in which the whole numbers represent the sub- 
provinces and types, and the decimals, the phases. To illustrate: 
A soil has the number 726.5. The number 7 means that it occurs 
in the lowan giaciation, the 26 that it is bro\m silt loam, and .5 
that rock. is found less, than 30 inches below the surface. These 
numbers are convenient for use upon the soil maps in numbering 
small soil areas. 

Peats consisting of 35 per cent or more of organic matter sometimes 

mixed with some sand, silt or clay. 

1. Deep peat — with peat more than 30 inches in depth. It is best 

drained by open ditches because of the uneqvial settling of tile, 
thus getting them ovit of line. 

2. Medium peat on clay — with peat between 12 and 30 inches in depth. 

Tile drains are usually below the peat and therefore have a 
good bed. 

2.1 Medium peat on clayey sand. 

2.2 Medium peat on sand. 

. ' 2.4 Medium peat on gravel. 

2.5 Medium peat on rock. 

2.6 Medium peat on marl. 

3. Shallow peat on clay — ^\vith peat 6 to 12 inches deep. It may be 

plowed sufficiently deep to bring up some clay for supplying 
potassium. 

3.1 Shallow peat on clayey sand. 

3.2' Shallow peat on sand. 

3.4 Shallow peat on gravel. 

3.5 Shallow peat on rock. 

3.6 Shallow peat on marl. 

Peaty loams — consisting of 15 to 35 per cent of organic matter with 
a large proportion of sand and very little silt or clay. 
10. Peaty loam on clay. 

10.1 Peaty loam on clayey sand. 

10.2 Peaty loam on sand. 

~ 10.4 Peaty loam on gravel. 
10.5 Peaty loam on rock. 
Mucks — 15 to 35 per cent of decomposed organic matter mixed with 
much clay and silt. 
13. Muck on clay. 

13.1 Muck on clayey sand. 

13.2 Muck on sand. 
13.5 Muck on rock. 

Clays — soils with more than 25 per cent of clay, usually containing 
much silt. 

15. Drah clay. 

15.1 Sandy drab clay. 



16. Oray clay. 



15.2 Gravelly drab clay. 

15.3 Drab clay on sand. 



SUB-PROVINCES, CLASSES, TYPES AND SURVEYS 115 

Clay loams — soils with from 15 to 25 per cent of clay with much 
silt and some sand. 

20. Black clay loam. 

20.1 Sandy black clay loam. 

20.2 Gravelly black clay loam. 

21. Drab clay loam. 

21.2 Drab clay loam on sand. 

22. G7-ay clay loam. 

23. Bed broirn clay loam. 

24. Yelloio gray clay loam. 

Silt loams — soils with more than 50 per cent of silt and less than 15 
per cent of clay, mixed with some sand. 

2'5. Black silt loam. 

25.1 Black silt loam on clay. 
26. Broivn silt loam. 

26.1 Brown silt loam on clay. 

26.2 Brown silt loam on sand. 

26.4 Brown silt loam on gravel. 

26.5 Brown silt loam on rock. 
2'7. Brovyn silt loam over gravel. 

28. Brotcn-gray silt loam on tight clay. 

29. Drab silt loam. 

29.1 Drab silt loam on clay. 

30. Gray silt loam on tight clay. 

31. Deep gray silt loam. 

32'. Light gray silt loam, orv tight clay. 

32.1 White silt loam on tight clay. 

33. Gray-red silt loam on tight clay. 

34. Yellow-gray silt loam. 

34.1 Yellow gray silt loam on clay. 

34.2 Yellow gray silt loam on sand. 

34.4 Yellow gray silt loam on gravel. 

34.5 Yellow gray silt loam on rock. 

35. Yelloio silt loam. 

35.1 Yellow silt loam on clay. 

35.2 Yellow silt loam on sand. 

35.4 Yellow silt loam on gravel. 

35.5 Yellow silt loam on rock. 

36. Yellow-gray silt loam over gravel. 

37. Yelloiv-broicn silt loam. 

44. Yellow-gray fine sandy silt loam. 

45. Yelloio fine sandy silt loam. 

Loams— soils with from 30 to 50 per cent of sand and with less than 
15 per cent of clay. No one constituent predominates sufficiently to impart 
very definite characteristics. 

50. Black mixed loam. 

50.1 Black mixed loam on clay. 

50.2 Black mixed loam on sand. 
50.5 Black mixed loam on rock. 

51. Brown loam. 

51.1 Brown loam on clay. 

51.2 Brown loam on silt. 

51.3 Brown loam on sand. 

51.4 Bro\ATi loam on gravel. 

51.5 Brown loam on rock. 



116 SOIL PHYSICS AND MANAGEMENT 

52. Gray loam. 

53. Yellow loam. 

54. Mixed loam — usually first bottom land. 

Sandy loams — soils with 50 to 75 per cent of sand and less than 15 
per cent of clay. 

60. Brown sandy loam. 

60.1 Brown sandy loam on clay. 

60.2 Brown sand}' loam on sand. 

60.4 Brown sandj' loam on gravel. 

60.5 Brown sandy loam on rock. 

60.6 Light brown sandy loam. 

61. Black sandy loam,. 

62. G'>-ay sandy loam. 

64. Yellow-gray sandy loam. 

64.4 Yellow-gray sandy loam on gravel. 

64.5 Yellow-gray sandj^ loam on rock. 

65. Yellow sandy loam. 

65.5 Yellow sandy loam on rock. 

66. Broion sandy loam over gravel. 

67. Yellow- gray sandy loam over gravel. 

68. Brown-gray sandy loa.in on tight clay. 

Fine sandy loams — soils with from 50 to 75 per cent of fine sand and 
with much silt and less than 15 per cent of clay. 

70. Black fine sandy loam. 

71. Brown fine samdy loam. 

71.5 Brown fine sandy loam on rock, 

72. Gray fine sandy loam. 

73. Mixed fine sandy loam. 

74. Yellow-gray fine sandy loam. 

75. Yellow fine samdy loam. 

76. Mixed sand and loess. 

77. Brown fine sandy loam over sand. 

Sands — soils with more than 75 per cent of sand. 

80. River sand. 

81. Dune sand. 

82. Beach sand (Lake Michigan) 

83. Residual sand. 
86. Fine dune sand. 

Gravelly loams — soils with 25 to 50 per cent of gravel with much 
sand and little silt. 

90. Gravelly loam. 

Gravels — soils Avith more than 50 per cent of gravel and much sand. 

95. Gravel. 

Stony loams — soils containing large numbers of stones over one inch 
in diameter. 

98. Stony loam. 

Rock Outcrop. 

The complete t3^pe nnmber may be formed in each by prefixing 
the number of the area or sub-province in which it occurs. 

SOIL SURVEYS. 

In order to make a scientific study of soils and to apply the 
knowledge to practical agriculture, it is very desirable that the 
samples studied be taken from areas that are representative of more 



SUB-PROVINCES, CLASSES, TYPES AND SURVEYS 117 

than a single farm. The study of a sample that is ordinarily sent 
in by a farmer for analysis means little to the agriculture of a 
state or even a county. The samples must be taken from areas that 
represent some distinct type of soil and care must be taken to avoid 
errors due to local variations. In order to place the sampling and 
analysis of soils upon a truly scientific basis, a soil survey in which 
the different types of soil are located on a map should be made, 
and the samples secured according to the types shown by the soil 
maj). 

Soils are sufficiently uniform and constant in texture to be 
divided into distinct types with fairly well defined boundaries, and 
a soil survey consists in working out these boundaries in the field 
and locating them on a map. The type is the unit of the soil sur- 
vey. The soils are examined to a depth of iO inches by means of 
an auger, and the variations not only of the surface but also of sub- 
surface and subsoil are noted. In some cases where the deeper sub- 
soil is peculiar and affects drainage, the examination may extend 
to a depth of 80 inches. This applies especially where sand or 
gravel subsoils occur. 

Surveys in Different States. — Some soil survey work has been 
carried on in every state. It was begun in 1899 and since then 
479,059,000 acres, or 35.2 per cent of area of the United States, have 
been surveyed. The soil survey of one state, Ehode Island, has 
been completed. Kearly all of the work that has been done has been 
in cooperation with the Btireau of Soils, this organization furnishing 
half the men and their expenses, while the state does an equal 
amount. In a few cases, as in Kentucky and Illinois, survey work 
has been done independently of the Bureau of Soils. In the latter 
state, 60 per cent of the entire area has been surveyed. 

1. Objects of a Soil Survey. — The objects of a soil survey may 
be stated as follows: (a) to take an invoice of the agricultural 
resources of a country, for they depend first of all upon the soils ; 
(b) to provide a scientific basis for consistent soil investigation so 
that time may be used to the best advantage in studying the various 
types and problems; (c) to furnish a basis for intelligent recom- 
mendations for permanent soil improvement; (d) to give the farmer 
who desires to study and improve his soil the information necessary; 
(e) in many counties to give to the county agriculturist a valuable 
asset to aid in his work ; and (f ) to give a basis for the introduction 
of new crops or farm practices. If the work ceases with the mapping 



118 SOIL PHYSICS AND MANAGEMENT 

of the soils, very little of real value is accomplished, as the soil 
survey is only prelimijiary to a more complete investigation. If, 
however, the soils are analyzed, field experiments carried on. reports 
published giving the results of the work, and recommendations for 
improvement and management made, the farmer may avail himself 
of all this information for improving his soil and his farm manage- 
ment generally. 

'-?. Methods of the Survey. — For the application of this infor- 
mation to the individual farm, it is necessary that the maps showing 
the soils of the farm should be accurate in all details. To accom- 
plish this, three things at least are necessary : first, careful, well- 
trained men to do the work; second, an accurate base map upon 
which to show the results of their work ; and third, the means nec- 
essary to enable the men to place the soil type boundaries, streams, 
etc., accurately upon the map. 

For work in the field each man must be familiar with the soil 
types and their variations in the area he is surveying; he carries 
an auger for examining the soil to a depth of -10 inches, a map of 
the area made to the proper scale mounted upon a small, smooth, 
light board. Where a satisfactory base map is not available, one 
must be made before the mapping is begun or as the work pro- 
gresses. A compass is carried to enable him to keep his directions, 
and he should be an expert at pacing distances and keeping his lo- 
cation. The mapper should have pencils for drawing in soil boun- 
daries and other features, and coloring soil areas. A traverse plane 
table should be within easy reach to be used for getting the direc- 
tion of roads and railroads. If buggies are employed the odometer 
may be used for measuring distances along roads or the revolutions 
of the wheel may be counted. 

The party consists of two men who work side by side. It has 
been found necessary, in order to get the detail with sulficient ac- 
curacy, that all areas must be traversed and every ten acres in- 
spected. To facilitate this, each section on the map used is divided 
into 40-acre plots and these form the most convenient unit area for 
work. 

Certain lines are selected that form the center of the work, such 
as a section line in one case and a half section line in the other, and 
each man works an area one-half mile in width, inspecting the soil, 
locating and indicating on his map the soil boundaries, roads, 
streams, railroads and any other features that should be shown. 



SUB-PROVINCES, CLASSES, TYPES AND SURVEYS 119 



%^ 



ar it 



Fig. 64. — Soil Samplers: (1) one-inch field auger; (2) one and one-half inch sampling 
auger; (3) rods for extension of auger for examining deep subsoil; (4) King sampling tube; 
(5) hammer for forcing tube into soil and bar for lifting it out again. 



120 



son. PHYSICS ANO MANAGEMENT 



In soiHo rasi^s aroas ol' five acro^ or ovoii kv^v^ are shown, but only 
when the aroa is a \ovv distinct tvpo. In s«tatos whoro no land 
tjurvoys have boon tnado iho roads form oouvoniout Hues from whioh 
to work. 

o. Sampling of Soils. — In ool looting soil san\ples for analysis 
each iuvostigator has \isod liis own method. rniforn\ity is very de- 
sirable for purposes of eomparison. J^inee the samples are to be the 
basis of investigations and plans for soil imin-ovemeut, it is highly 
important that they shonUl )j)e representative of their respei'tive area 
or type. AVhatevor the stratum division-^ u\ade. they slumld be se- 
cured without mixing or eoutamiuatiou in any way. ^'arious de- 
viees have been used, but the soil auger (Fig. (M), 40 inches long. 
seeu\s best for the purpose in humid climates. 

The total depth to which the sample is taken varies with the 

Weight of Soil Strata 







Pounds per awro 






Tliii-kuosi:, inches 


Saads 


Tests 


Clays, ela.v 

loauis, silt 

loams, loHuis 

and sand}' 

loaius 


A 
1 


Surf:v(.v 




•-\:^w.wo 


l.tXX).lXX1 


2.1XX).(XX) ^ 



13^ Subsurface ! 5.000,000 

I 
I 
I 



2,000,000 



4.0011.000 



20 Subsoil 
i 



7,500,000 



3,000,000 



6,1X10.000 



^ 



SUB PROVINCES, CLASSES, SOILS ANT) TYP1<:S 121 

characicr ol' Mic soil jiikI inii'itosc lor which il is collociud. In arid 
I'cii^Mons s;iiii|)liii^' is rrcqutiiiliy (htiic lo a dcpIJi oi" iU feet, especially 
for iiKiisI lire (IcterniiiiatioiKs, while in linniid regions 40 ii)cheKS ia 
snllicicnl. 'I'lu^ divisions ai'e freciuenily made in (J-, S)-, or VZ-lnch 
de|)ilis, rc,<4;ir(llcss of any natiii'al divisions in the soil. At the 
Illinois M\|)crinicnl, Sl;ilion Ihc s;ini|)l('S ai'c; iiikcni with a \ y^- 
iiicli ;iii;4('i- lo a. dc^pth of 10 inches. Tlu! samples ai'e divided into 
(;i) siii'tacc soil, (i% inches in deplli, ahoiit as dee|) as plowed, 
and representing- an iippro.xininic wi'i^'hL of 2,000,()0() |)ounds pel' 
acre for I he common clays, clay loams, silt loams, sandy loams and 
loams; (h) the sulisiii'Tace sti'atnm, ()-/•>, to ;i() inches in d(!ptli, 
twice the tlii(;kness ol' tlu! sui'facc! and rcipnsseiiting approximately 
a weight of I, ()()(), ()()() ponnds ])er a(;re ; and (v) tin; suhsoil, 20 to 
10 inches in deplli and weighing approximatc^ly (i, 000, 000 ponnds 
j)ei' aci'e. hjacli of the three samples is pnt into a, separate; hag a,nd 
analyzed sc^pai'aldy. 

Hands are the heaviest soils and peats iind mucks arc; lightest, 
the latter two heiiig only- half as heavy as the toj'iiier. The weights 
of the strata are gixcn in the preceding tahle. 

I'liese divisions do not always represent the natural strata in the 
soil, hiit the depth of 20 inches is usually near the natural line of 
cha.nge helvveen suhsurfacc! and suhsoil, and aJtliough there is no 
elia,ng(! at 40 inches yet thai, is a. vei'y convenient point, since itgiv(!S 
the three strata with a relativti ihickness of 1, 2, nnd ;!. 

'^^riu; sample should he composite, and this is much more; im- 
portant for the surface than either of the other strata, since it may 
have heen modified mon- or less by tillage oi- other treatment. At 
the Illinois h]\|)eriment Station the surface sainide is secured from 
12 to l(i dill'erent borings nt some distance apart, hut all from the 
same t(Mi acres. The suhsui-face and suhsoil are seeured from (! to 8 
d liferent Ixn'ings. 

QUESTIONS 

L Dcfiiic il siil)-|)r()viiu'i'. 

■J.. Wliiit is llu' basis upon wliicli classes arc made? 

;f. Wlial t'iictois ari' taken into account in maicinj^ soil ty])es? 

4. What is the system of soil nomenclature as used l)y the Bureau of 

Soils? 
.'). What is the significance of color in naming soils? 
(i. How are "on" and "over" used in naininy soils? 
7. Define peats. 

5. Delinc dce|), medium and sliallow jx'at. 
1). Define peaty loams and nnudvs. 



122 SOIL THYSICS AND MANAGEMENT 

10. lUnv do olays ditVor from flay loams? 

11. Dit^tiiiiiuiish botwoon silt loams and loams. 

12. What avo tho olassos of samis? 

13. Why should oavo be oxeroised in tho soUvtion of samples for study? 
1-4. Ciive the objects of a soil survey. 

15. Why should tho surveyor examine the soils to a depth of SO inches? 

U>. What is necessary to nutke the soil map valuable? 

17. What apparatus is neeessj\ry for the soil surveyor? 

IS. How are samples taken? 

10. To what depth are they taken and what divisions are made? 

20. What preca tit ions are to be observed in takiTig samples? 

21. What is a composite sample? 

22. What is the weight of the strata of peat ? Of sand? 

REFERENCES 

Soil Report.?, Illinois Station. 

yield Operations of the l^ureatt of Soils. U. S. D. A. 

Kentucky Station lUilletins Ul-2. !!>;>. 1!U. l!>o. 

Iowa Station Rulletin S-. UH^o. Iowa Soil Survey Keport. No. 1. liUT. 

Soil Survey Keports. Wisconsin Survey Bulletins Nos. •J8-40, i;Uo-l4. 

Ohio Koivnuoissance Soil Survey. Field Operations Bureau of Soils. 1012, 

Missouri Station Research Bulletin o. 1010. 

rennsvlvania Station Bulletin lo2. Soils of Bennsylvania, 1014. 

^liehiiran Oeolocical auvl B^iolosiical Survey. Publication 7, Geological Series 

5; Pttblication 0, Geological Series 7. 
Tennessee Station Bulletin, vol. x. No. o, 1S07. 



CHAPTER X 
MINERAL CONSTITUENTS 

I. SOIL PARTICLES AND THEIR SEPARATION 

The forces at work on rocks break them down into soil material, 
the particles of which are of various sizes and shapes. The relative 
proportion of tlie dilferent sizes is a very important factor in the 
character of a soil. As a general rule where soils contain large per- 
centages of a certain grade of particles, one or two per cent makes 
very little difference in the physical phenomena that take place. It 
is, however, of considerable importance to know the approximate 
physical composition or texture, as it usually gives some idea of the 
capillary power, aeration, percolation and other properties of the 
soil. 

There are frequent exceptions to this, however. The physical 
composition gives no idea of the arrangement of the particles or 
structure of the soil, 'l^he aggregation of the particles into granules 
or crumbs plays a most important part in the physical phenomena 
that take place. Some expression for showing this is very desirable. 

Mechanical or physical analysis, which is the process of sepa- 
rating a soil into the dilTorciit grades of particles according to size, 
is an attempt to accomplish this. 

As yet, however, no very scienl^ific grouping of the soil particles 
has been devised. That of Dr. Hopkins is without doubt one of the 
best, as it recognizes a constant factor or ratio, the square root of 
ten, between groups. In other methods or schemes the ratio be- 
tween grades varies quite widely. The result is that when an 
anal^'sis is made of soils of a regularly decreasing or increasing size 
of particles no uniformity is shown. 

Several systems have been devised, of which the principal ones 
in this country are given in the accompanying table. 

It will be noted that in the 0s1)0Tne system the factors vary from 
3 to 6; in the Bureau of Soils from 2 to 10 ; in Hilgard's from 1.3 
to 3 ; in the Hopkins system the constant factor is 3.16 or the square 
root of 10. 

123 



124 



SOIL PHYSICS AND MANAGEMENT 



Different Systems of Physical Analysis, icith the Grades and Ratio or Factor 

Between Grades ' 





Osborne 


Hopkins 


Bureau of Soils 


Hilgard 


Number 


Grades 


Factor 


Grades 


Factor 


Grades 


Factor 


Grades 


Factor 


of group 


mm. 




mm. 




7/1 m . 




m m . 




1 


3.000 




1.0000 




2.000 




3.000 




2 


1.000 


3 


0.3160 


3.16 


1.000 


2 


1.000 


3 


3 


.500 


o 


0.1000 


3.16 


0.500 


2 


0.500 


2 


4 


.250 


•-> 


0.0316 


3.16 


0.250 


2 


0.300 


1.^6 


5 


.050 


5 


0.0100 


3.16 


0.100 


2.5 


0.160 


1.87 


6 


.010 


5 


0.00316 


3.16 


0.050 


5 


0.120 


1.33 


7 






0.0010 


3.16 


0.005 


10 


0.072 


1.65 


8 












0.047 


1.53 


9 














0.036 


1.30 


10 














0.025 


1.44 


11 














0.016 


1.56 


12 








1 


0.010 


1.6 



1. Methods of Mechanical or Physical Analysis. — {a) The 
Sieve Method. — The sieve method is used as a part of practically 
every system for the separation of gravel and some or all grades 
of sand. It consists of using sieves with openings of the required 
size for making the necessary separation. The separations may 
be made dry or by. washing the material through with water. The 
latter is preferable. 

(b) The Subsidence Method. — The soil to be analyzed is 
thoroughly disintegrated by shaking ^\■ith Avnter containing a few 
drops of ammonia. It is then passed through a battery of sieves 
to remove the sand and gravel. The water with the fine material in 
suspension is then placed in a wide-mouthed bottle and the finer 
grades are decanted first. This is accomplished by filling the bottle 
such as sho^\^l in figure 65 to a certain mark with water and allow- 
ing it to stand sufficiently long for the coarser grades to settle below 
the mouth of the tube. The supernatant liquid with its gTade of 
soil particles is then blown oft" through the tube B by forcing air 
through the tube -i. The contents of the bottle are stirred and 
sufficient time is allowed for the coarser particles to subside again. 
As the sands tend to carry the fine material down -^ith them this 
operation must be repeated several times. The same thing is done 
for each of the other grades. The microscope is used to determine 
whether the proper size is being removed. The great amount of 
time required is a serious objection to this method. 

(c) Schone's Elutriator Method." — The method of separating 
soil particles by currents of water of varying velocities was first 



MINERAL CONSTITUENTS 



125 



applied by Nobel in his apparatus given in figure GG. This "was not 
very satisfactory aiid the same principle was applied somewhat dif- 
ferently by Schone in his elutriator. The apparatus consists of a 
conical glass tul)e, as shown in figure 67. The sample, after 
thorough disintegration and passing tlirough sieves to remove the 
coarser material, is placed in the tube and a current of water allowed 




Fio. 65. — Bottle for Subsidence Method of mechanical analysis. By forcing air into the 
bottle through A, the water with the suspended particles is forced out through JS to the level 
of C. 



to enter at G. It is evident that the size of the particles carried 
upward and through the outlet tube will depend upon the rate of 
flow of the water, and by regulating this the separations are made. 
There are some inaccuracies in this method caused by counter-cur- 
rents in the elutriation cylinder and the tendency of the particles 
to collect into granules. In order to overcome this, Hilgard devised 
his churn elutriator. 



126 



SOIL niYSICS AND MANAGEMENT 



{d) The Chum Elutriator Method of Hilgard/' — Thit^ con- 
i>ist55 of ail apparatus? a!> !?ho\vu in tiguro i^S. Tlie soil in suspension is 
placed in the base ot" a eyliudrieal tube wliieU eonrains a vapidly ro- 
volvinii' stirrer. Water is foreed into the basse of the tube in 
amounts sutlieient to create an U]nvard current just vapid enough to 
earrv out the tiuest particles. \\ hen these are removed the rate of 

Fui. 66. 



Fig. 67. 




Fu;. 6S. 




f 



./ 



Fig. 66. — NoWl's Flutri.^tor. The suspotidtnl soil is plaooil in C .ind allowed to t'ow 

thrvHuth the c<.nuo;d slasses 1. 2. S, and 4. sivius tivo different grades. 
Fig. 67. — Sohone's Klutriator. The water enters at t? and the grades are collected at /v. 
Fig. (^. — Hilgarvi's Churn Elutriator. 

the current is increased and another grade is carried out. A screen 
Wtwt\ui the stirrer and the separating chamber prevents the agita- 
tion of water in this chamber. In this way all separations except the 
finest particles are made. Particles of clay less than 0.00'.?3 mm. 
must be separated by subsidence. This is done by allowing the 
larger particles to subside for '^4 hours and then decanting the day. 



MINERAL CONSTITUENTS 



127 



(e) Centrifugal Method/ — The centrifugal method has been 
perfected by llic liureau of Soils and is now used more extensively 
ill this country than any other. 'I'he machine for this purpose is 
shown ill ii"-ure G9. It consi.?ts of a centrifuge suspended from the 




Fig. 09. — Mtichinu for centrifugal analysis of soils. Bureau of Soils, U. S. D. A. 




Fig. 70. — Yoder's Centrifugal Elutriator. 



sliaft of an electric motor. The sample to be analyzed is defioccu- 
lated by shaking with water containing a few drops of ammonia. 
This requires from two to thirty hours. The clay and silt are sepa- 
rated from the sands by subsidence and decantation or by sieves. 



128 



SOIL PHYSICS AND MANAGEMENT 



/n 



nf 




ii 



The water containing tlie silt and olav is pur in tost tubes and 
whirled at a speed of about 1000 revolutions per minute. The time 
neoessarv to throw down the silt is determinal bv mieroseopio exami- 
nation of the material in sus|Hnision. After deeanting- the clay re- 
maining- in suspension, the test tube is tilled with water, the sediment 
is stirred and the operation repeated until the elav is all removed. 
By running the eentrifuge at a slower rate or shorter time another 
grade may be left in suspension and deoanted. 

{i) Yoder's Centrifugal Elutriator.-"' — One of the bt^t ma- 

ohines for physical analysis is 
Yoder's, in which he has com- 
■' bined the principles of the ivn- 
trifuge and the elutriator, as 
shown in figure TO. The par- 
ticles are subjected to two forces, 
the centrifugal tending: to throw 
them down and the hydraulic 
carrying them upward. The 
centrifugal etfect is exerted to a 
greater extent upon the i>oarser 
particles and the hydraulic upon 
the finer. By this combination 
a more rapid separation may bo 
accomplished. The appai-atus 
consists of an ehitriating bottle, 
B. into which the suspended soil 
Fu;. 71.— Kuvs's aspirator for the determi- is' placcd after the sauds are re- 

moved. Water enters at F, and 
the overflow with the sediment 
is colhvted in the tube T. While it does its work very thoroug-hly 
and quickly, it is a very expensive and a rather delicate piece of 
apparatus. 

(g) King's Aspirator Method/' — King was of the opinion that 
ordinary mechanical analyses do not furnish a basis for determining 
any very important data for soils. The arrangement of the particles 
into groups is of much conse<|uence in pliysical phenomena, but 
mechanical analysis does not indicate the structure. In order to 
overcome this ditficulty he worked out the method for finding the 
" etfective diameter " of soil particles. The grouping of particles 
upon which the percolation of air and water and other phenomena 
depends is t^xken into account. The rate at which air passes through 
a cv^lumn of air-dried soil of a given cross section and length under 



o 



nation of tho effeotive iliameler of soil parti- 
cles. 



MINERAL CONSTITUENTS 



129 



standard conditions ol: tein|)('ratuixvaii(l prcssiu'c gives the data by 
whicli tlic diameter is (leterniiiu'd. The soil is ])iaced in D, figure 
71, a lube liaviii-;- a. capacity of 1»)<) t)i- "iCD c.c. willi a wire gauze 
bolU)ni. This is eojuiecLed by means of a tube io Ihe aspirator A. 
A cord vvitii a weight attached exerts sulTicieiit '' pull " to draw the 
air through Ihe soil. The "ell'ective diameter" is deduced by 
means of a roi'iiuila using the data determined. The ilow of water 
Ihi'ough the soil conipulcd i'l'oni llie '^effective diameter" obtained 
corresponds \c'ry closely to that actually observed, as shown in the 
table. 

Comparison Between Computed and Observed Flow of Water 



Grade of sand 


lOfToi'tivo diameter 
ol particles 


Computed flow of 
water 


Observed flow of 
water 






mm. 


Gms. 


Cms. 






8 


2.54 


2,277 


2,296 






7 


1.808 


1,132 


1,090 






6 


1.451 


757 


756 






5K 


1.217 


522 


542 






5 


1.095 


453.2 


504.6 






4 


.9149 


297.5 


329.2 






3 


.7988 


193 


210.0 






2 


.714G 


122 


• 138.6 






1 


.()()()() 


80.6 


94.8 









.r)i()9 


(IG.S 


72.3 





11. AIIXICKAL SOIL CONSTITULXTS AND TWFAll I'UOPEltTIES 

.1. Colloids. — Wbilc the colloids of soils are usually classed 
along with day, their iniporlaiict! juslides sepai'ate ti'eatment. Al- 
though not as abundant in soils as many other constituents, yet 
they possess such tlistinctive characteristics and impart these so 
noticeably that the,v are of the greatest consecpieiu'c not only from 
a physical standpoint but from a chemical and biological as well. 
Non-colloids are called crystalloids. 

Colloids are sul)stances com])oscd of the very finest of; ])articles 
and when mixed with water api)ear to go into solution. Wlien con- 
taining a certain amount of water tliey appear jelly-like or gelati- 
nous. Since the colloidal state is de|)endent upon the size of parti- 
cles, it follows that many substances may exist in both colloidal and 
crystalloidal forms. Up to the present time only about -100 sub- 
stances have been fonnd that exist in- both. 

Examples of Colloids. — The word colloid is dcriNcd from rnlJa, 
meaning glue. A glue or jelly-like consistency is one of the most 
familiar characteristics of colloids. In the inorganic world almost 



130 SOIL PHYSICS AND MANAGEMENT 

all metals and metalloids have been produced in a colloidal state. 
The simplest compounds of these, as oxides, sulfides, chlorides, 
hydroxides, some carbonates, chromates, phosphates, sulfates, and 
silicates, occur in this form. Among the organic substances that 
occur as colloids are starch, dextrin, gum, rubber, glue, gelatine, 
caseins, albumins, humus, and proteins in general. 

Properties of Colloids. — The difference between colloids and 
crystalloids in one of physics and not of chemistry. The chemical 
composition is the same in whichever state they occur. Hence, a 
study of colloids is largely a study of their physical properties and 
characteristics. 

(a) Size of Particles. — The upper limit of size for colloids is 
near the limit of visibility with the ordinary high-power microscope, 
which is not far from 0.0001 mm. With the most powerful micro- 
scope some of the largest colloidal particles may be seen ; with the 
ultra-microscope, particles 0.000005 mm. in diameter are about the 
limit of visibility. Many smaller particles exist, but their presence 
is revealed only by the properties of their suspensions. The parti- 
cles larger than 0.0001 mm. give ordinary suspension and may some- 
times show some properties of colloids. Those between the above 
size and the molecule give colloidal suspensions, while the molecules 
give true solutions. 

The smaller the particle the longer it will remain in suspension. 
This is due to the fact that the specific gravity of the particle and 
its adhering film of water have such a low specific gravity that it 
varies but little .from that of water (see page 35). 

(b) Broivnian Movement. — Very fine particles in water are con- 
stantly in motion. This movement is not a definite progressive one, 
but an irregular, jerky motion from one side to the other. Particles 
as large as 0.01 mm. sometimes show a slow movement of this kind, 
but it is best developed in the very finest particles. The movement 
is increased by higher temperature. 

(c) Dialysis. — Dialysis is the diffusion of a substance through 
a membrane. Experiments show that colloids will not pass through 
membranes or at best only very slowly. Separation of colloids from 
crystalloids may be made in this way. 

From the following table it will be seen that dialysis takes place 
about 80 times as rapidly with crystalloids as with colloids. This 
is due to the fact that the parchment itself is a colloid. 

(d) Diffusion. — Colloids diffuse very slowly and they do not 
allow other colloids to pass into them. Crystalloids may pass into 



MINERAL CONSTITUENTS 



131 



or through them quite readily. Because of this lack of power to 
diffuse, colloids possess very little osmotic pressure. Pfefter gives 
the osmotic pressure of a one per cent solution of sugar as equiva- 
lent to a column of mercury 51.8 cm. high, while that of a one per 

Dialysis and Diffusion of Colloids and Cryslalloids 



Substances 



Crystalloids 

Sodium chloride. 

Ammonia 

Alcohol 

Glucose 

Cane sugar 



Amount 
dialyzed in 
equal times 



Times of 
equal diffusion 



Average. 



Colloids 

Gum arable . 

Tannin 

Albumin. . . . 
Caramel. . . . 



Average. 



1.00 
0.85 
0.47 
0.36 
0.47 

0.63 



0.008 
0.015 
0.003 
0.005 

0.00775 



1.0 
0.6 
2.0 
3.0 
3.0 

1.92 



7.0 
11.0 
21.0 
42.0 

20.25 



cent of gum is only G.9 cm. From the above table it will be seen that 
crystalloids diffuse over ten times as rapidly as colloids. 

(e) Freezing and Boiling Poinis.— The lowering of the freezhig 
and boiling points by crystalloids such as common salt in solution 
is familiar to every one. The change in these is in proportion to 
the amount dissolved. Colloids have very little effect. Forty-four 
grams of protein dissolved in 100 grams of water lowered the freez- 
ing point only 0.06° C.^ 

(f) Electrical Behavior.— Colloids are poor conductors of elec- 
tricity as compared with crystalloids, and their conductivity de- 
creases with the amount of colloid in the disperse medium. Any 
substance in contact with water and many other liquids acquires an 
electric charge. Most substances become negatively charged in con- 
tact with water. The charge can be varied and even reversed by 
electrolytes and may even become zero at certain suitable concen- 
trations. If a current of electricity is passed into a colloidal solu- 
tion, the particles migrate to one pole or the other. If they migrate 
to the negative pole (cathode) they are positive, and if toward the 
positive pole (anode) they are negative. The colloidal conditioii 



132 SOIL PHYSICS AND MANAGEMENT 

exists as louii" as the ehargo is the same. This eondition is not coii- 
tined to colloidal particles alone, hut to coarser material in sus- 
pension. 

It' an electrolyte is added to the solution and the ions and 
particles carry opposite electric charges, tloccules are formed which 
settle to the hottom. If the ions and colloidal particles have the same 
electric charges the colloidal condition is maintained. If two col- 
loids of opposite charges are hrought together, mutual precipitation 
will take place, and if thev are the same their stahility will be in- 
creased. In adding an electrolyte to completely precipitate a colloid 
a sutlicient amount must he added so that the charge of one exactly 
neutralizes the charge of the other. 

(g) Adsorption. — Adsorption is a surface phenomenon and 
hence any increase in the total amount of surface area will increase 
the adsorption. Colloids possess this property to a high degree be- 
cause of the large total area of the small particles, ^^'hen a solid 
is exposed to a gas a certain amount of gas adsorption occurs. When 
a solid and a liquid come in contact, concentration occurs on the in- 
terface between tiie two. This concentration is known as adsorp- 
tion. All substances are not equally adsorbed by colloids. The 
same is true of all ions. If potassiimi chloride is passed through a 
soil more of the potassium ions will be adsorbed than of the chlorine. 

(h) Slirinl-age. — The property of shrinkage is very character- 
istic of cololids (see Fig. 72). 

Colloids in Soils. — The colloids in soils consist of both organic 
aud inorganic or mineral substances. 

(a) Organic Colloid-s. — Some of the various forms of humus 
constitute the organic colloids and probably form the larger part 
of colloids in many soils. These are formed as a result of bac- 
terial action in the process of humification. Part of the organic 
matter is broken down into such minute particles as to form coHoids. 
The amount is constantly changing in the same soil. Since gTanu- 
lation takes place more perfectly in the spring than at any other 
time of the year, it would seem that there is a greater supply in the 
soil at this time than at other periods. This may apply to mineral 
colloids as well. The adsorptive power of these organic colloids for 
water is of great economic importance in soils. Schlossing states 
that one per cent of calcic humate (colloidal) has as much cement- 
ing power as 11 per cent of plastic clay. 

(b) Mineral Colloids. — Mineral colloids are found most abun- 
dantly in fine-grained soils such as clays and clay loams. The col-. 



MINKIUI. (JONS'l'I'I'llI'lNTS 



133 




134 SOIL ruYSics and management 

loids consist largely of forrio oxiJo, ferric hydmte, silicic acid and 
In dratcd aluminuii\ silicate. 'These are formed in tlie decomposition 
of rocks. In the decomposition ot" most feldspars the silicic acid 
aiid {Uumimuu silicate are formed, Init not all in a colloidal state. 
Zeolites easily give rise to colloidal silica. While many substances 
exist in a colloidal state in soils, yet the total amount is not large. 
Warrington estimates it at never over two per cent. 

V. Clays and Clay Loams. — Alineralogically clay is com- 
ptTised largely of kaolinite, a hydrous aluminmu silicate that is 
formed from decomposition of alnminous minerals. In addition, it 
may ci^ntain very tinely divided particles of quart?., feldspar or other 
minerals. In fact, clay may be composed entirely of other 
minerals tluvn kaolinite, although this is not usually the ease, 
rhysically. clay etmsists of particles U\?s than 0.00 1 nnu. in diameter 
(Hopkins^, 0.005 mm. (Bureau of Soils) or 0.000;> mm. (llilgard) 
(see table on paiiv I'M"). This is divided into two parrs, which may 
l>e called clay proper, consisting of particles large enough to be dis- 
tinguished with the microsci->pe, about 0.0001 mm. in diameter, and 
a small amount of hydrous aluminum silicate whose particles are 
very small and constirute part of the mineral colloids. 

(a) Tenacity. — Tenacity is that quality of cohesiveness by 
which snbstai\ees resist disruption, imparting more or less stability 
to them. Tn soils this property is due primarily to colloids. Clays 
and clay loams, however, possess this property to a high degree. 
Soils have been divided according to their tenacity into " heavy *' 
and " light.*' A '' light " soil is one that works easily, as sand or 
peat, and incidentally has a high s{^>ecitie gravity, as sand, or a low 
specitic gravity, as ^H\it, but all possessing very little cohesiveness. 
*• Heavy " soils, on the other hand, are those containing a great deal 
of elav, and hence possessing a high tenacity. Cl^ys, clay loams, 
and heavy silt loams and some sandy loams aiv examples of these. In 
absolute Aveight they are not as heavy as the sand soils, but the 
greater tenacity possessed by them makes thetn more dithcult to 
plow. ITence the term " heavy " is applied to them. 

A high moisture content decreases tenacity. However, a medium 
amount of moisture imparts a high degrtw as does also an extremely 
small amount of moisture, as where tlie soil bewmes dry and cloddy. 
This is due to the hardening of colloids and the deposition of soluble 
salts as a cementing material between the soil particle*. The tenac- 
ity of " heavy" soils may be diminished by the addition of or- 



MINERAL CONSTITUENTS 



135 



gallic lualkM-, ami in general hy aiiylliiiig, as lime, that will produce 
granulalioii. 

(h) Shrinkage. — Clay ])c>,^scsscs the property of shrinkage to a 
rcmarkiihic degree, due (o ilu! lows of moisture from the particles 
in geiioriil but the colloidal (H)nstitucnt particularly. This shrinkage 
is eni[)luisi/ied. when a largo amount of humus is present, because 
the luimus is partly colloidiil. ('lay has been found to shrink 31.9 
per cent, and })eat ;52.(i per cent (see axxioinpanying table). Ilenfe 
a soil composed of bolh of these will possess the 2)roperty of shrink- 
ago to a great, and sometimes injui'ious degree. 

Shrinkage of Soils of VaHed Physical Composition, with the Moisture and 
Organic-Mailer Content ' 



Soils 



Sand 

Yellow fine sandy loam 

Brown sandy loam 

White silt, loam 

Brown sill, loam 

Black clay loam 

Drab (day 

Peat 



Total 
organic matter 



per cent 

0.75 
0.80 
2.90 
0.79 
4.88 
5.50 
3.60 
64.40 



Moiaturo 



•per cent 

9.67 
21.39 
17.43 
23.69 
31.93 
40.83 
61.94 
193.94 



A real 
shrinkage 



per cent 

1.88 

2.48 

4.94 

4.11 

10.26 

19.00 

31.93 

32.64 



This ])roperty is fre(piently del I'inieiilal to crops, l)eeaiise of the 
formation of large cracks that tear the roots of the ])laiits as well as 
cause excessive loss of moisture ( Figs. 72 and T;i). The property of 
shrinkage is a primary cause of granulation, and this is only pos- 
sessed by soils which contain colloids. Tt is also an aid to percola- 
tion and drainage, because the cracks produced by shrinkage do not 
close entirely, thus leaving ])assagewa_ys for water. During the 
dry summer of 1914, a clay loam shrank to such an extent that an 
inch auger could be pushed into cracks without any effort to a depth 
of 24 to 28 inches. The cracks undou1)tcdly extended to a depth 
of 30 inches. 

(c) Plasticity. — A moist clayey soil may be molded into any 
form or iH-essed into thin jdates, retaining the shape indefinitely. 
The property permitting this is called plasticity. The degree of 
plasticity vari(>s directly as the amount of colloids ]iresent. Tt is not 
a desirable quality for soils to possess, as such are liable to b(> more 
readily puddled. The amounts of shrinkage, hygroscopic watcM- and 
adsorption are approximate indications of tlie plasticity of clay soils. 



136 



SOIL PHYSICS AND MANAGEMENT 



Highly plastic soils become very hard upon dryiug. Plasticity may 
be diminished by organic matter, granulation or change of texture. 
Plasticity may be increased by the breaking down of soil gran- 
ules into their individual soil particles. While this is detrimental to 
soils, it is of decided advantage to the ceramist. 

(d) Puddling. — Clays and clay loams are usually made up of 
crumbs or granules, composed of many soil particles united by a 
weak cementing substance, such as humus or some other colloid. If 

the soil is worked or trampled 
by stock when wet these granules 
are broken down, the colloids be- 
come somewhat uniformly dis- 
tributed throughout the mass 
and an impervious condition re- 
sults. The soil is puddled. 
Water or air will not penetrate 
it and a worse condition could 
not well be produced. The pres- 
ence of sodimn carbonate or 
black alkali, or the long-con- 
tinued application of certain 
fertilizers, such as ammonium 
sulfate or sodium nitrate, brings 
about a puddled condition. Some 
clay and clay loam soils are pud- 
dled naturally. This is likely 
to be the case if they are strongly 
acid and low in organic matter. 
Water in a soil acts as a lubri- 

-Cracks in black clay loam after Caut and mOVCmCUt takeS place 

period. Photographed August, j^-^Qj.g readily bctwecn the par- 
ticles. It also softens the 
cementing material so that the granules are easily broken down. 
When the soil is turned by the plow a shearing, slipping movement 
is produced as it curves over the mold board. This will pulverize it 
if in good condition, but puddle it more or less if wet. "\ATien a 
heavy animal steps on the dry soil it is compacted, but if wet the 
foot sinks into the soil, causing a movement which breaks down 
many granules, thus puddling the soil. 

Wlien puddling is produced in a heavy soil it may be almost 
worthless for a time, but the natural agencies of f reezingr and thaw- 




FiG. 73. 
a long dry 
1916. 



MINERAL CONSTITUENTS 137 

ing and wetting and drying will gradually restore the soil to its 
granular condition. The time required for this depends somewhat 
upon the organic matter and lime content of the soil. It is never a 
wise plan to permit stock to run on a moderately heavy soil when 
wet so late in spring that its granular condition will not be restored 
again by freezing and thawing. In the corn belt considerable dam- 
age is done to the soil by pasturing the cornstalks too late in the 
spring. 

(e) Coagulation or Flocculation. — The examination of a clay 
soil usually shows it to be made up of fine particles cemented into 
granules, crumbs, or grains. If a few grams of clay soil be pul- 
verized and put into a liter of water and stirred and allowed to 
stand for several weeks, some material will be found still in suspen- 
sion. If some mineTal acids or certain salts or lime water are added 
to this liquid coagulation will occur and floccules may be seen form- 
ing, which gradually settle to the bottom, carrying with them the 
suspended clay particles. This may be well shown by puttiilg a 
drop of water with suspended clay under the microscope. Intro- 
duce a drop of lime water under the cover glass. The particles will 
at once begin to collect in groups, showing the formation of floccules. 
This process takes place in soils due to the presence of certain sub- 
stances in solution in the soil moisture- that act as electrolyi;e&. In 
some cases, fertilizers when added produce this effect, and lime- 
stone, which gives rise to the soluble bicarbonate, produces floccula- 
tion. This is, however, a slow process and will not produce granula- 
tion as quickly as is ordinarily supposd, although heavy acid soils 
are undoubtedly benefited physically by the application of lime- 
stone. Common salt produces the same effect and likewise many 
other salts. Most alkaline substances, however, deflocculate clay 
soils and produce a puddled condition. Ammonia and most of its 
salts are good examples. The black alkali of the West is especially 
detrimental because of the physical effect it has on soils in producing 
a puddled, impervious condition. This, however, may be remedied 
by the application of gypsum, calcium sulfate. The injurious effect 
of sodium carbonate or black alkali is destroyed by this reaction 
and sodium sulfate and calcium carbonate produced, the latter of 
which has a flocculating effect on the soil and soon changes the 
puddled condition entirely. It has been observed frequently that the 
water of glacial streams is extremely muddy, while that coming from 
limestone regions is characterized by clearness. The difference is 
due to the lime content of the water from the two sources. In 



138 SOIL PHYSICS AND MANAGEMENT 

regions where limestone is absent and where the sediment of streams 
comes from acid soils the water is rarely clear. Even stock ponds 
in regions of acid soils where the water is seldom disturbed never 
become clear. 

While clay soils are difficult to manage, due to the danger of 
puddling when too wet and from clods when too dry, vet with 
proper care, drainage, incorporating organic matter and maintain- 
ing the supply of limestone, the condition of these soils ma}' be im- 
proved so they work fairly well. In addition to the flocculation 
produced by the substances mentioned above, natural causes hasten 
it. Wetting and drying, and freezing and thawing, will change the 
character of the soil from a cloddy to a granular condition, or cause 
it to " slake.'' The alternate expansion and contraction of the col- 
loidal material, whether of mineral or organic origin, tend to break 
the soil into granules. Fall plowing is especially desirable on 
'- heavy '' soils that are well drained, because of the good tilth 
developed during winter by these natural agencies. If a clay soil 
becomes cloddy it is practically impossible to reduce it to a condition 
of ijood tilth by any mechanical means, but if freezing and thawing 
occur, or a shower falls, working it under the right moisture con- 
ditions will break the clods easily into masses of granules. 

3. Silt and Silt Loams. — Silt is divided into three classes, 
fine, medium, and coarse, ranging in size from 0.001 to 0.032 
mm. in diameter (Hopkins), 0.005 to 0.05 m. (Bureau of Soils) or 
0.01 to 0.07 mm. ( Hilgard) . The particles of tine silt are sufficiently 
small to give to soils properties somewhat similar to those of clay, 
but -sdthout so much danger of puddling. Silt enables soils to 
retain much moisture and gives great capillary power, and hence 
forms some of the best soils for resisting drouth. They are suf- 
ficiently coarse, however, to permit of fair aeration, but not to an 
excessive degree, as in V y case of sands. The silt loam soils cover 
extensive areas in the middle west of the United States and owe 
their origin to the loess. 

They possess sufficient tenacity to give the necessary stability, 
but not enough to cause them to work with any great difficulty. The 
shrinkage, liowevi -, is not usually sufficient to produce very in- 
jurious eifects. Since gi-anulation depends upon the amount of col- 
loids present, and since organic matter as well as clay may furnish 
this constituent, the silt loams containing the largest amount of 
organic matter granulate best. Silt soils deficient in organic matter, 
such as CTay or yellow timber soils, show little or no granulation 



MINERAL CONSTITUENTS 139 

and may be easily reduced to a powder or dust made up of indi- 
vidual particles. These run together badly with heavy rains. 
, 4. Sands and Sandy Loams. — Sand is divided into three 
groups, fine, medium, coarse and sometimes very fine, varying 
from 0.032 to 1 mm. in diameter (Hopkins), 0.05 to 1 mm. (Bureau 
of Soils), or 0.12 to 1 mm. (Hilgard). Sand possesses very little 
tenacity, hence little stability. There is usually great danger of 
movement by the wind and in many cases sand soils are seriously 
damaged in this way, as Is seen in the " blow-outs " in sand areas 
(see p. 59). This movement may be prevented by incorporating 
organic matter which imparts sufficient tenacity to hold the sand. 
The fine and medium grades of sand allow fair moisture movement 
both up and down, but the coarse allows too much percolation, while 
capillary movement is exceedingly limited. It is generally believed 
that sands are very deficient in moisture and that the " firing " of 
corn on sandy lands is always due to this cause. Often, however, 
it is due to a lack of nitrogen, the drying of the lower leaves being 
produced by translocation of nitrogen to carry on further growth in 
other parts of the plant. This drying of the leaves may be almost 
entirely prevented by supplying the crop with the necessary food. 
The fact that sands do not retain much moisture enables them to 
warm up early in the spring. 

5. Gravel and Gravelly Loams. — Many types of soil con- 
tain considerable percentages of gravel. It is of very little use 
except that through its extremely slow decomposition it furnishes 
a small amount of plant food. It may form a part of any type of 
soil, but is more commonly associated with the coarser constituents. 

6. Stones. — Stones are quite common in many soils of the 
glaciated and residual areas, but have very little value except to 
modify temperature and conserve moisture to a slight extent. 
Their slow decomposition may provide a small amount of plant 
food. 

QUESTIONS 

1. What benefit is a knowledge of the physical composition of soils? 
2', What is meant by mechanical or physical analysis ? 

3. Why is the Hopkins method considered superior to others ? 

4. Note the different factors or ratios between the grades. How much do 

they vary? 

5. Should these factors be constant? Why? 

6. How is the sieve method used? 

7. Explain how the separations are made in the subsidence method? 

8. What is the principle of Schone's elutriation method ? 



140 SOIL PHYSICS AND MANAGEMENT 

9. What advantage does Hilgard's method possess over Sehone's? 

10. What efl'eet does whirling the sample in the centrifuge have? 

11. What is the principle of Yoder's machine? 

12. What is the advantage of King's aspirator? 

13. Describe the method of King. 

14. What is the importance of colloids in soils? 

15. What are colloids? 

16. Why may substances be in both colloidal and crystalloidal forms? 

17. Give examples of inorganic colloids. 

18. Give examples of organic colloids. 

19. Does colloidal condition depend upon physical condition or chemical 

composition ? 

20. What about the size of particles in colloids? 

21. Why do small particles remain in suspension so long? 

22. What is Brownian movement? 

23. What is dialysis? 

24. What difference in the dialysis between colloids and crystalloids? 

25. Discuss diffusion of crystalloids in comparison to colloids. 

26. What effect do colloids liave upon the freezing and boiling points of 

liquids? 

27. What is peculiar in the electrical behavior of colloids? 

28. What effect does an electrolyte have upon the colloids? 

29. When will an electrolyte completely precipitate clay in suspension ? 

30. What is adsorption? 

31. Is it uniform for all substances? 

32. What are the organic colloids in soils? 

33. What are the mineral colloids? 

34. What may be the mineral composition of clay ? 

35. What is tenacity? 

36. Define a " light " soil. A " heavy "" one. 
3?. What is the effect of moisture on tenacity? 

38. How may the tenacity of soils be diminished ? 

39. What causes soils to shrink? 

40. What benefit is derived by shrinkage? What disadvantage? 

41. Define plasticity. 

42. How may plasticity be increased? Diminished? 

43. What is the condition of a puddled soil? 

44. What effect does water have on ease of puddling? 

45. Why does plowing tend to puddle a wet soil ? 

46. What agencies destroy a puddled condition? 

47. Why is fall plowing of hea\y soils beneficial ? 

48. What advantages do silt soils possess over clays? 

49. \Miat about shrinkage and granulation of silt soils? 

50. Why does sand possess little tenacity ? 

51. Wliat effect does this have? 

52. Wliat is '■ firing" of corn and what is the cause? 

53. What value has gravel in soils? 

54. What value have stones in soils ? 

55. Define tenacity. 

56. Of what value are colloids in soils? 

57. What property causes black clay loam to " roll '" upon wagon wheels? 



MINERAL CONSTITUENTS 141 

REFERENCES 

^ Briggs, L. J., Martin, F. 0., and Pearce, J. R., Bulletin 24, Bureau of Soila, 
U.S.D.A., The Centrifugal Method of Soil Analysis, 1904, p. 33. 

* Wiley, H. W., Principles and Practice of Agricultural Analysis, 1906, n. 

231. ^ 

=• Op. Cit., p. 246. 

* Bulletin 24, Bureau of Soils, 1904. p. 12. 

'Yoder, P. A., Bulletin 89, Utah Station, The Xew Centrifugal Soil 

Elutriator, 1904. 
"King, F. H., Physics of Agriculture, 1907, p. 121. 
'Zt. f. phys. Chem., Leipsic, 9, 88 (1802). 

* Unpublislied data, Soil Physics Division, University of Illinois. 

General References. — Fletcher, C. C, and Bryan, H., Bulletin Si, 
Bureau of Soils, U.S.D.A., Modification of the Method of Mechanical 
Analysis, 1912'. Rohland, Paul, Tlie Colloidal and Crystalloidal States of 
Matter, 1914, D. Von Nostrand Co., New York. Hatschek, Emil, An Intro- 
duction to the Physics and Chemistry of Colloids, 1913, J. & A. Churchill, 
London. Ostwald, translated by Fischer, Hand)x)ok of Colloid-Chemistry, 
1915, P. Blakiston's Sons & Co., Philadelphia. 



CHAPTEE XI 

ORGANIC CONSTITUENTS OF SOILS 

By far the most valuable constituent of soils is the organic mate- 
rial derived from the plants and animals that have lived in and 
on the soil. The term organic matter will be used to include all 
material from organisms, to distinguish it from the term humus of 
more restricted use. Humus refers, in its restricted meaning, only 
to that portion of organic matter that is soluble in dilute alkali. 

Kinds of Organic Matter. — Organic matter exists in the soil in 
every stage of decay, from that whose cellular structure is still visi- 
ble, to that very similar to coal. It may be divided into (a) active 
or fresh, which decompo'ses readily; (b) the inert, which is usually 
old and decomposes too slowly for the use of crops; and (c) the 
coal-like material that oxidizes with extreme slowness, if at all, and 
whose chief use is to impart a dark color to the soil (Figs. 74 and 
75). The active is the most important and is that form which is 
ordinarily supplied to the soil as manure and legumes. Under long- 
continued, injudicious systems of cropping the active organic matter 
is largely removed and the result is exhausted, " run-dovra " or 
" worn-out " land. To maintain the productiveness the organic 
matter must be supplied in considerable quantities and of a form 
that will decay readily. It is equally essential to supply organic 
matter in a more stable or less readily decaying form, as straw, 
corn stalks or other non-leguminous material, since these benefit the 
soil physically for a longer time than legumes. 

Amount of Organic Matter in Soils. — The organic-matter 
content of soils varies quite widely in the same locality. Even in 
soils from which it has not been removed by erosion a distance of 
a few rods may make a great difference in the amount. Soils con- 
tain from a small fraction of a per cent to 90 per cent. Swamp 
lands generally contain most, while sand soils contain least. 

How much organic matter a. soil should contain is a question 
ofteij asked and one very difficult to answer. A soil may contain 
five per c?nt of organic matter and be less productive than one with 
only two per cent. Much depends upon its activity or rapidity of de- 
composition. The chances for large yields are decidedly in favor of 
the soil with a large organic content. A soil with a few tons of fresh 
142 



ORGANIC CONSTITUENTS OF SOILS 143 

or quickly decaying organic matter, such as clover or manure, may 
give better results than a soil full of old, slowly decomposing organic 
matter unless the conditions are most favorable. There should be 
sufficient organic matter to keep the soil in good physical condition 
and also furnish nitrogen for maximum crops. The organic con- 
tent depends upon several factors, as follows: 

(a) Moisture exerts a double influence in aiding the accumula- 
tion of organic matter in soils. In the first place, it is favorable to 
the growth of plants. It makes very little difference how little or 
how much moisture is present in the soil, some plants have adapted 
themselves to growing" under those conditions. Even where water 
stands nearly all the year, cat-tails, flags, sedges, and some grasses 

Fig. 75. 




" ■ # ^' ' y^ 

FiQ. 74. — Fragments of plants found in soils. (Bulletin 90, Bureau of Soils.) 
Fia. 75. — Fragments of insects found in soils. 

grow luxuriantly. In the second place, the presence of excessive 
moisture tends to preserve the plants, which ultimately form soil 
themselves or become mixed with the mineral matter and aid in 
forming soil, such as peats, peaty loams, and mucks. Even soil with 
an ordinary amount of moisture prevents complete oxidation of the 
roots and other fresh vegetable material that becomes incorporated 
with it. Soils containing small amounts of water, such as sands 
provide very favorable conditions for oxidation, and hence the 
organic-matter content of such soil is low. 

Overflow land generally contains more than the adjacent upland 
because of the greater growth due to a richer soil, the better facilities 
for its preservation because of greater moisture content, and the 
deposition of some organic matter along with the sediment during 
periods of overflow. This deposit may cover leaves and grasses, thus 
preserving them from complete decay. 



144 



SOIL PHYSICS AND MANAGEaiENT 



Arid soils are naturally low in organic matter because the moist- 
ure is not surticient to produce a large growth of vegetation. 

(b) Vegetation, — The upland timber soils contain much less 
organic matter than the adjacent prairies. It is safe to assume that 
the prairies were much more extensive formerly than now. Xewly 
formed lands were originally treeless and covered by smaller plants, 
but nuu*e especially grasses. This was particularly true in the glaci- 
ated area. The prairies were covered with grasses whose network 
of roots extended to a depth of S to "20 inches or more. A sample of 
virgin blue stem prairie sod on brown silt loam contained roots at 
the rate of 13% tons per acre to the depth of 6% inches. Part of 
these roots died each year, and the partially decayed material 
accumulated in the soil, forming the black prairie soils of the corn 
belt. In Illinois the analyses of 303 samples show the surface soil to 
a depth of 6--^ inches 'to contain -i.53 per cent, or about -to tons of 
organic matter per>acre. This includes the rolling and flat prairie 
soils, but not the swamps. The subsurface, G-g to '^0 inches in depth, 
showed an organic-matter content of *"-?. 8 per cent. 

That this ie -probably true as to the origin of the black earth soil 
or chernozem of Eussia is "well shown by the following table which 
gives the relative amount of roots and percentage of humus in six- 
inch depths-: 

Roots and Humus in Three Chernozem Soils at Different Depths. The Roots 
in the Surface Six Inches is Taken as 100 Per cent ^ 



Depth 


1 


2 


3 
















Roots 1 


Humus 


Roots 


Humus 


Roots 


Humu3 


0- 6 inches . . , 


100 ' 


5.42 


100 


8.11 


100 


9.64 


6-12 inches . . . 


89.1 


4.83 


63.9 


5.19 


80.3 


7.77 


12-18 inches . . , 


66.9 


3.62 


48.3 


3.92 


70.0 


6.71 


18-24 inches . . . 


47.3 


2.56 


35.0 


2.84 


58.4 


5.81 


24-30 inches . . . 


47.3 


2.50 


26.0 


2.11 


38.2 


3.57 


30-36 inches . . . 


34.6 


1.88 


18.1 


1.47 


33.0 


3.18 


36-42 inches . . . 


23.9 


1.29 


6.3 


.51 


16.2 


1.56 


42-4S inches . . . 


14.4 1 


.78 




.70 






48-54 inches . . . 


6.7 i 


.36 












These determinations are rather t}"pical for semi-arid or rather 
sub-humid prairie soils where there is a g-reater tendency for the 
•rix>ts to penetrate deeply. A similar condition exists in humid soils, 
with this difference, that the great mass of roots is nearer the surface. 

The invasion of the prairies by forests has been going on very 
slowly. The first trees to spread over the prairies were wild cherry, 



ORGANIC CONSTITUENTS OF SOILS 145 

black walnut, hackberry, elm, ash, aud bur-oak. The shade of the 
trees and the undergrowth tliat slowly crept in killed the grasses, 
and the plants that replaced them supplied very little organic mat- 
ter to the soil. The leaves and twigs accumulated upon the surface 
and decayed completely or were burned by forest fires. The organic 
matter that had accumulated was slowly being removed by oxidation 
of nitrification, with the result that the soils were gradually changed 
until a light-colored soil resulted. When this change had taken 
place the trees mentioned above were gradually replaced by white 
oak, hickory, and others adapted to light-colored soils or soils low in 
organic matter. Several generations of trees were required to effect 
tliis cliange. So great was the reduction of organic matter that the 
timber soils contain less than half as much as the prairie. The anal- 
yses of 164 samples of timber soil show 1.93 per cent in the surface 
and 0.77 per cent in the subsurface. 

(c) Limestone. — Soils rich in liipestone are usually well sup- 
plied with organic matter, due to the fact that limestone encourages 
a larger growth of vegetation, especially of legumes, and is very 
effective in retaining humus in the soil against leaching. 

(d) Latitude and Altitude. — As a general rule soils of north- 
ern latitudes have more organic matter than those of southern. 
While the conditions for a luxuriant growth of vegetation are not so 
favorable in the north, yet the conditions for its preservation are so 
much better that the result is a larger organic content. This is well 
shown in Illinois. The deposit of loess in the State along the Mis- 
sissippi Eiver is the same throughout the length of the State. The 
analyses of eight samples of deep loess from the south end of the 
State show 1.11 per cent of organic matter, while four samples from 
the north end show 3.86 per cent. Eighteen samples of timber soil 
from the south end of the State show 1.5 per cent of organic matter 
in the surface and 0.58 per cent in the subsurface, while the same 
general character of soils in the north shows 2.4 and 0.96 per cent 
respectively. The same is true of the prairie soils. The brown 
prairie soils from the lattiude of the southern part of the early Wis- 
consin glaciation show 4.5 per cent, while the same type 150 miles 
to the north contains 6.1 per cent. 

Changes of Organic Matter. — When vegetable matter becomes 
mixed with soil it undergoes a physical change produced by bacterial 
action in which the plant tissues are destroyed, and it becomes a 
black or dark brown homogeneous mass. At the same time a chem- 
ical ehange takes place. The process at first is quite rapid, but later 
10 



146 



sou. rinSlOS ANP MANAOVMKNT 



luHHMiios voiv slow, ami still ktor oouiJos* almost ontirely. The supply 
of oxygon IS somowhat low in tho soil and tho oonditions aro not 
favorable for annploto oxidation of tho vogotablo matter. The 
|>{\vtial oxidation pnnluees ovjianie matter of varied imposition. 
In {his ehaniiv (he hydi\\5ivn and oxyjjen iHMitent of the veiivtahle 
matter hoi'vnnes less, while the ptvportion of earhon and nitroiivn 
inert^ises. The orsi'at\ie matter of the soil iu\der ditVerent ei>nditions 
may v.>ntain from thiw to twenty times as nvueh nitrosivn as the 
wi^uiiial matoriaK This ohaii^syt^ may l>o carried so far that ultimately 
earlHUtiKed material may W pn^lvuvd that is similar to eoal or ehar- 




Fivj- 



X ,.,0 ,..'. ■ouiut in #v\U*, 
vUv»lU>uu 5KK liutvjwi ^tf" Soils.) 



-<>iHwiuu>MN v»t v-T^s-U iv>uuvi m «.\mI*s 

iwiP (Figs. Tl> aud tT). This dvKs? not uudergv further ehai\go. 
The humus aivumulaies moiv rapidly in very moist soils than in 
iHnnparatively dry oi\es. 

The following table frvmi Hilgiird shows*the changes in the for- 
mation of coi\l, pn>l>{\bly somewhat similar to those changvs of 
onjjvnio matter in soils : 






V '" (\k«I * (Jtfo».sf«re and Ash Omittied 
ns) 



l>?*t 



Cy»sas 



lose 



Uunuu Blown 1 

I Mtd httiHifi J 

scad I 8ar> 

faw ! 
^I'hnin'* 



BUirl; 



40 






brown 



:(Uint 
SO I txvJ '■ bill*- u„,>.„ 
ittclieg kBov«j)| nuiwvi*'**iV™^' 



ultra 



avrlxMx * 44.44 -U).4-<».T 57.5^1 62,00 1^1,10 6l\r>0 S4.20 c^.^50 

Uvvit\>snn\ ) lUT 2.5-4,5 5,40 5.20 5-1X1 5.iH> 5.S0 2,60 

0\Ysivn j 40.SS S5,S-47.S SlVW S0.70 26,S0 24.1X1 S.StI \ .> ^^^ 



Nit^^4iXM\, 



,S-1S,7 .v^l 2a0 4.10 .iXl; 1.20 I 



ORGAN I(J CONSTITUENTS Ol'' SOILS 



147 



Wliil(; this iiihit' dotis ii(;t represent exiU'lJy ilio changes tliat lake 
place in the soil under all conditioiiK, yet Schriner and lirowri 
have shown that many particle,-! of coal and chnreoal-liko material 
exist in I he soil, indiitating that this j)roc(;ss prohjthly occurs in soils. 
Home of Ihis may he l.lu! rcisult of (ires. 

Nitrogen Content of Humus. — Moisliire plays a v(!ry impor- 
tiint part in dciierniinin*;' IIk; coniposiiion of or^;uii(; rnalter of soils, 
in(li(')din<j;' llud, lli(( process of luimificjiiion is (jiiiie v.iried under 
(lid'ei'cid. condilions. This dillei^MKu^ is well shown in IJh! nil,i'()<f(!i) 
contenl, of litinuis from arid and liiinnd r(!<^ions. Ilil^^'ard hns'shown 
that soils of (fidiforiiia vary in liiumis cotdcint with the riiird'all, hut 
(heir niiro^-(!n iippeiU'S lo Ix; iiidcp(;ndeni of liunddity. 

Humus and Nitrogen Content of Humid and Arid Soils of California ' 





Humus 


NitroKen in 
hurriut) 


Nitrogen in 
soil 


Arid soils, Calif oriiiji 


pur cant 

.91 
1.00 
2.45 


per cent 

I5.2:i 

8.38 
5.29 


per cent 


Sub-irrigated arid, (Julifornia 

Humid soils, California 


.099 
.135 



Later investigations secun to jndictate that the nitrogen content 
of tlu! hunms in arid soils is not as high as the ahove figures show. 
Th(! organic matter of humid regions contains a somewhat Viiri- 
ahle amount of nitr()g(!n. One hundred and twenty-six surface sam- 
])les of prairi(! woils (!ontained 5.1 per cent of organic matt(!r, the 
nitrogen of which was approximately 4.88' per cent. I^he average 
organic-matter content of 39 surface samples of timber soils was 1.93 
per cent, which contained 5.09 per cent of nitrogen. By multiplying 
the nitrogen content of a humid, soil ])y 20 a fair ap[)roxim;ition 
of the amount of orgjinic matter may be obtained. 

The character of soil humus will also depend upon the character 
of the materiiil from which it is d(!rived. Snyder, of Minnesota, has 
determined the amount of nitrogen in humus from different sources. 
The Amount of Nitrogen in Humus from Different Materials '' 



Humus from uioat scraps . 
Humus from }i;n!(',n clover, 
llumus from ciow maiiur(>,. 
Himnis from oat straw. . . , 
Ilvimus from sawdust 



10.90 per cent nitrogen 

S.94 j)er cent nitrogen 

O.IC) per cent nitrogen 

2. .50 per cent nitrogen 

.32 per cent nitrogen 



Distribution of Organic Matter in the Soil Strata. — The con- 
tent of organic matter diminishes with depth in all normal soils so 
that at from three to six feet the amount becomes very low. In arid 



148 



SOIL rUYSlCS AND ^MANAGEMENT 



soils the eoiitont nins more imit'orm and to i^roatov Jopth. duo to 
deeper root de\elopiuei\t. l.u t^waiup t^oils there is frequently a 
great ueeumulatiou in the surt'aee aiul upper subs^urt'aee, Avith rather 
a stiddeu decrease at a distinct- line. Timber soils show a greater 
decrease in the snbsnrface than prairie soils. T!\e organic matter 
is nsiially dee^H^r in filluvial soils than in others. The distribntioii 
depends to a large extent npon the depth of rov>t developnient, the 
effect of bnrivwing animals, the accumulations that are taking place 
as in bottom and -swamp lands and the cracks produced by shrink- 
agw which is especially characteristic of clay and clay loam soils. 

Organic Matter in Soil SinUa * 



Soil types 




Brown silt la-vn\ 

Bl;u'k day io;in\ 

\'olloNv-gray silt loam 

Yellow silt loam 

Gi-ay silt loam on tight day 




Surface 
0-6 2/3 
iaehes 


Siibsurface 

fi 2/3-ao 

inches 


p«r e«nt 

5.30 


3.10 


7.03 


3.58 


2.33 


o.so 


1.70 


o.w> 


2.40 


1.31 



Subsoil 
21V40 
inches 



■per cent 

0.91 
1.02 
0.57 
0.4S 
0.70 



Value of Organic Matter to Soils. — It is next to impossible 
to assign a detinite money value to organic matter as in the 
case of tiitrogen, phosphorus, and potassium. The difficnlty arises 
from the fact that \hen incorporated with the soil it has sev- 
eral ditferent effects, physical, chemical, and biological, any one of 
which is of suflficient importance to justify its itse. The value of 
org-anic matter must in the end be determined from the value of the 
increase in crops produced. This has been worked out for manure 
and is being determined for other forms of organic matter, such as 
crop residues and legumes. The thing"s for which it is of value are 
as follows : 

1. Granulation is one of the most important properties of heavy 
and medium soils. This gives permeability for Knh air and water, 
and very desirable working qualities that heavy, non-graimlar soils 
do not posse«!S. In fact, some of the most intractable soils are clays 
that are quite low in organic matter. The granular structure lessens 
the tenacity. This latter is esptvially noticeable in heavy soils. 
There is no one constitttent so beneficial to such a huge class of soils 
as organic matter. Its removal from a soil destroys its power to 
granulate almost entirelv. When the humus is taken from brown silt 



ORGANIC CONSTITUENTS OF SOILS 



149 



loam and black clay loam 1)y loucliiiig with dilute ammonia, the 
power to granulate is lost. 

Figure 78 siiows llie cfl'ect of remo\al of humus ujjon the granu- 
lation of black clay loam and drab clay. "^JMie silt loams granulated 
very little even with organic matter. Each soil has been wet and 
dried several times. Cropping with the continued removal of 
organic matter will ultimately bring about a condition of poor 
granulation and. consc<pK'ntly poor tilth. 

3. Retaining Moisture. — There is no better method of increas- 
ing the moistui'e liolding capacity of soils tlian by adding organic 




Fio. 78. — The effect of the removal of humus and of wetting and drying upon granula- 
tion. Drab clay is the only one that shows any tendency to granulate when humus is re- 
moved. (University of Illinois.) 

matter. It acts as a spcmge itself, and when mixed with the mineral 
part of the soil gives Jiigher porosity and consequently greater water 
capacity. It retards capillary movement in soils, as well as aids in 
the production of a better mulch, both of which help in retaining 
moisture by reducing evaporation. Sand permits of rapid percola- 
tion with comparatively small amounts of water retained. If organic 
matter is added to sand, the retentive power of sand will be greatly 
increased. This ta})le shows the effect. 

Effect of Organic Matter on Retention of Moisture in Sand * 



Soil material 


Grams of 

water retained 

by 100 grams 


Increase, 
per cent 


Coarse sand 


13.3 
18.6 
24.7 
40.0 
184.0 




Coarse sand with .5 per cent peat 


40.0 


Coarse sand with 10 per cent peat 


8.5.7 


Coarse sand with 20 per cent peat 


200.7 


Peat 


1283.4 







150 SOIL PHYSICS AND MANAGEMENT 

The movement of capillary moisture is principally along the 
surfaces of mineral soil particles that are in contact, and the more 
points of contact the larger the amount and the greater the rapidity 
of movement. Organic matter introduces many very irregular par- 
ticles which diminish the number in contact. As a result capillary 
movement is slow in soils rich in organic matter. 

3. Puddling. — The particles of soils low in oTganic matter are 
not cemented together into crumbs and hence are free to move. 
When these dry soils become wet there is a rearrangement of the 
particles, due to the drawing force of the surface film, by which they 
are brought closer together, and the pore space is so diminished that 
water cannot penetrate the wet stratum very rapidly. This is spoken 
of as "running. together," but is really one form of puddling. The 
change is produced by the tension of the film of water drawing the 
particles together. This action may be seen where drops of water 
fall in dust during a shower. 

Soils low in organic matter are easily puddled if worked when 
wet, and a longer time is required for the natural agencies to correct 
this condition than if the soil is well provided with organic matter. 
Since granules are destroyed by puddling a correction of this con- 
dition is produced when by any means granulation is restored. 

4. Prevents Loss by Erosion. — Erosion causes very serious 
loss on many soils. A vast amount of the richest soil material is 
removed annually from the rolling land by the excess of rainfall 
that runs off as surface drainage. The more the run-off the greater 
the amount of washing. It is practically impossilile to prevent this 
entirely. The loss may be diminished by methods given in 
Chapter xxvii. 

5. Increases Temperature. — Organic matter imparts a darker 
color to the soil, thus increasing the absorption of heat, and raising 
the temperature, and, as a general rule for well-drained soils, the 
darker the soil the higher the temperature. Light-colored soils are 
cold, while dark ones are warm. This difference in color may 
increase the temperature from four to ten degrees F. at a depth of 
four inches during a clear day and give the crop on the dark soil a 
distinct advantage. 

6. Biological Effects.- — Biological and consequently chemical 
action is increased by organic matter, not only because it provides 
a food supply for the organisms, but also because it brings about 
physical conditions favorable to the action of bacteria which produce 
chemical action. 



ORGANIC CONSTITUENTS OF SOILS 151 

7. Furnishes Nitrogen to Crops. — The only source of nitrogen 
for our non-legumiuous crops is organic matter, Xitrogen starva- 
tion goes liand in hand with low organic content in soils. This is 
evidenced by the yellowish-green color of corn, oats, or wheat on 
eroded land deficient in organic matter in contrast to the dark green 
color where this constituent is abundant. It supplies nitrogen, the 
most expensive food element used by plants, one that we cannot 
afford to buy for ordinary farm crops. A 100-bushel crop of corn 
per acre requires 150 pounds of nitrogen, the commercial value of 
which at 15 cents per pound is about $23.50. Other crops require 
somewhat similar amounts. Legumes are independent of organic 
matter, as they obtain their nitrogen from the air. 

8. Binds Soil Particles Together. — On sandy soils well-decom- 
posed organic matter binds the sand grains together and reduces 
movement by wind. It also increases the water-holding capacity, as 
seen before. 

Losses of Organic Matter. — The amount of organic matter 
in the surface stratum of the ordinary upland soils varies from 
15 to 60 tons per' acre. This has required thousands of years 
for its accumulation, but through the systems of cropping generally 
practiced it is being removed from the soils much more rapidly 
than it ever accumulated. 

(a) By Cropping. — The amount of organic matter removed 
annually from a soil well supplied with it in reasonably active form, 
such as brown silt loam, is not far from three-fourths to one ton per 
acre. A large portion of this is used indirectly by the crop, while the 
remainder is lost by the natural processes described below. In com- 
paring a virgin prairie soil with the same soil after cropping for 
sixty years, it was found that the organic-matter content of the soil 
has been reduced approximately fifty tons per acre. Of course, in 
soils with a smaller amount of organic matter the total removed is 
necessarily less. The amount removed depends to some extent upon 
the crop grown. The inter-tilled crops use more nitrogen, and more 
organic matter would be decomposed to produce it than non-tilled 
crops. It must be remembered that loss of nitrates either by crop- 
ping or leaching means loss of organic matter from the soil. 

(b) By Erosion. — Organic matter may be removed from the 
soil by erosion. Very few regions are so flat or have the soil so well 
protected that there is not more or less erosion taking place, and in 
the more rolling areas this becomes a very active agent in the 
removal of the organic matter along with the soil. In this way in 



152 SOIL rilYSlCS AND iMAXAGEiMENT 

oortaiu regions alinost all of the suri'aeo soil and its? organic matter 
have been removed, and yelknv " olav points " are quite common. 
These are nothing more tluui the outcropping of a stratum, either 
of subsurface or subsoil, which contains little or uo organic matter. 
Even on brown silt loam areas nuich loss of organic matter takes 
place through erosion, and this becomes more serious the longer 
cropping courinuos. 

(c) By Leaching, — In tiie partial decomposition of vegetable 
matter soluble organic acids are formed. These may be removed iu 
part by the water wliicli percolates through the soil during heavy 
rains. This is especially true of acid soils. It is not uncommon to 
see the drainage water of peat bog's of a brownish color, due to the 
dissolved org-juiie matter. The presence of small amounts of certain 
alkalies, as annnonia and sodium carbonate, increases the solvent 
power of water for humus. 

(d) By Fires. — Fires of even moderate intensity destroy large 
amounts of organic matter from the immediate surface, and even in 
the burning of straw, stubble, or corn stalks considerable organic 
matter is lost from the soil. Snyder' gives the following: "The 
soil from Hinckley, Minnesota, before the gi-eat forest tire of 1893 
showed .1.159 per cent humus and 0,12 per cent nitrogen. After the 
fire there were present 0.41 per cent humus and 0.03 per cent nitro- 
gen. The forest tire had cansed a loss of •■?o00 poimds of nitrogen 
per acre, or thirteen tons of organic matter," ^Euch organic matter 
that should be plowed back into the soil is burned. 

(e) By Oxidation or Nitrification. — The process of oxidation 
is carried on through the intluence of hicteria which are always 
present in fertile soils. Fnder favorable conditions of moisture, 
temperature, and aeration these org-jinisnis are very active agents in 
destroying organic matter. They are especially active in cultivated 
and well-aerated soils, and while their work means destrnction to 
orgwiic matter, they are at the same time performing a function 
absolutely necessary for the growth of plants. In the destruction 
of organic matter they are producing plant food essential for crops. 
In the growing of crops, one and one-half poimds of nitrogen are 
required for a bushel of corn, one for oats, and two for a bushel of 
wheat, and this must be obtained from orgimic matter through the 
agency of these bacteria. The greatest loss occurs when no crop is 
growing, and these soluble plant foods are lost by leaching, although 
some loss of nitrate? is coing on whenever drainage takes place. 

(i) By Use of Quicklime. — A very serious objection to 



ORGANIC CONSTITUENTS OF SOILS 



153 



burned limestone or quicklime is that it tends to destroy the organic 
matter of the soil, and most soils that need lime have too little 
organic matter to begin with. At the Pennsylvania Station the plots 
having burnt lime applied for 25 years showed less nitrogen by 
375 pounds than the limestone plot. This difference is equal to 
37.5 tons of barnyard manure per acre. At the Virginia Station it 
lias Ijeen determined that the applications of quicklime have reduced 
the amount of nitrogen and organic matter when compared with 
plots treated the same except that quicklime was omitted. 

(g) By Fallowing. — Fallowing is leaving the land without a 
crop for a season during which the soil is cultivated. This has been 
a very common agricultural practice in European countries, but 
more especially in England. The objects of the fallow were to 
destroy weeds, to develop an abundance of nitrates for the succeeding 
crop, to increase the moisture content of the soil, and to produce 
good tilth in heavy soils. While all of the objects were accomplished, 
yet in regions where heavy fall, winter, or spring rains occur much 
of the soluble plant food which was produced at the expense of 
organic matter was leached out of the soil and lost. King found 
that in the spring of 1900 land fallowed the previous season con- 
tained 245.7 pounds more of nitrates per acre than -the cropped 
land. The following table from Hall shows the effect of leaching 
from fallowed land upon the wheat crop : 



Yield of Wheat Grown When Percolation 


was Large 


and Smal 


8 




Percola- 
tion 
through 
60-inch 
gauge 


Bushels per acre 




Tile ran 
days 


Wheat 

after 

wheat 

each year 


Wheat 
after 
fallow 


Gain 
due to 
fallow 


15 years of percolation, 
below average 

16 years of percolation, 
above average 

Loss due to excess leaching 


3.99 
8.92 


4 
13 


30.1 

27.1 

3.0 


44.6 
29.3 
15.3 


14.5 

2.2 



Fallowing should be practiced only where the rainfall is not 
suflficient to cause any loss by leaching, as in sub-humid and semi- 
arid regions. 

Estimation of Organic Matter. — No very satisfactory method 
has been devised for determining the organic matter of soils, since 
it is impossible to determine it directly. 



154 



SOIL PHYSICS AND MANAGEMENT 



[i\) Loss on Ignition." — The ignition niotliod is sometimes 
iisod, but lit the best is only approximate for peats and sands 
wliieli contain very little water of hydration. Five grams of water- 
free soil is heated to low redness in a crucible till all organic matter 
is burned away. C'ool and moisten with a few drops of a saturated 
solution of ammonium carbonate. Dry and heat to 150° C. to 
expel excess of annnonia.' The loss in weight is the organic matter, 
water of hydration, and volatile substances. 



Loss on Ignition Compared with Organic Matter 





[Calcul-ited from organic carbon] 




Kind of soil 


Between 
100° and 
ignition 


Between 
120° and 
ignition 


Between 
150° and 
ignition 


Organic 

matter at oS 

per cent 

carbon 


Old pasture 


per cent 

9.27 
7.07 
5.95 

5.S2 


per cnit 

9.06 

6.SS 
5.70 
5.39 


per cent 

8.50 
6.55 
5.61 
■4.76 


per cent 

6.12 


New pasture 


4.16 


Arable soil 

Clay subsoil 


2.44 

0.65 



The per cent of loss on ignition is seen to be much higher than 
that obtained from the actual amount of organic carbon determined, 
taking the organic matter as containing 58 per cent of carbon or 
multiplying the per cent of carbon by 1.72-i. 

(b) Combustion in Oxygen.^" — The combustion method has 
been used to some extent. The soil is placed in a porcelain or plati- 
num boat and ignited in a combustion tube partly filled with cupric 
oxide. The tube is connected with a series of bulbs, those of sul- 
phuric acid for absorbing nitrous fumes and water and a weighed 
potash bulb for absorbing the carbon dioxide formed during com- 
bustion. xV current of air from which the carbon dioxide has been 
removed by passing through a potash bulb is drawn through the 
tube by means of an aspirator. The amount of carbon dioxide pro- 
duced is then determined by weighing the bulb, and the organic 
matter found by multiplying the weight of carbon dioxide by O.-lTl. 

(e) The Chromic Acid Method." — The apparatus consists 
of a train of flasks and bulbs arranged as shown in figmre 79. A 
current of air is drawn through the apparatus by an aspirator at /. 
The carbon dioxide is removed from the air by a solution of potas- 
sium hydroxide in the flask G. The combustion takes place in flask 
F, into which about ten grams of soil are placed, together with five to 



ORGANIC CONSTITUENTS OF SOILS 



155 



ten grams of pulverized potassium biclir ornate. II is a condenser. 
A contains a saturated solution of silver sulfate to absorb any hydro- 
chloric acid, sulphur trioxide or dioxide that may be generated. B 
contains concentrated sulfuric acid, C potassium hydrate, D acid 
to be weighed with C in determining the weight of carbon dioxide. 
An acid guard bulb completes the train. The air is allowed to 
pass through the system for about ten minutes. The soil and 
potassium bichromate are thoroughly mixed in F and concentrated 
sulfuric acid (specific gravity 1.83) slowly admitted through the 
dropping funnel until the end of the tube from G is covered. If 
no vigorous action takes place the flask may then be slowly heated. 
The heating should continue from five to ten minutes. The bulbs 
C and D are then weighed and the amount \ of carbon dioxide de- 




FiG.79. — Arrangement of apparatus for determining organic matter by chromic acid method. 
(Bulletin 24, Bureau of Soils.) 



termined. The organic matter is found by multiplying this by 0.4T1. 
This method does not seem to give complete combustion. A com- 
parison with, the. dry combustion method shows that the amount of 
carbon found by oxidation with chromic acid is about 79.9 per cent 
of that found by the combustion method. 

Carbon Found by the Two Methods in Soils Dried at 100° C'.^^ 



Kind of sail 



Combustion 

method 
with oxygen 



Chromic acid 
method 



I per cent 

Old pasture i 3.55 

New pasture I 2.41 

Arable soil 1 .42 

Subsoil 0.38 



per cent 

2.81 
1.93 
1.18 
0.28 



156 SOIL PHYSICS AND MANAGEMENT 

Determination of Humus/-' — Ten grams of soil are treated 
on a lilter successively with a one per cent solution of hydro- 
chloric acid until the lime is removed, as shown by testing a 
few cubic centimeters of the filtrate with annnouium oxalate after 
neutralizing with ammonia. W-asli the soil with distilled water to 
remove the acid. The filter and soil are placed in a bottle or stop- 
pered cylinder and a definite amount of a four per cent solution of 
ajumonia is added. The amount added should vary from 150 to 
500 cubic centimeters, depending upon the organic-matter content 
of the soil. Digest with frequent shaking for 13 hours and allow 
to stand for 13 hours. Filter the supernatant liquid and use an 
aliquot part of the whole for evaporation. Dry at 100° C, weigh, 
ignite and weigh again. The loss by ignition is the humus. Cal- 
culate the amount in the entire sample. 

QUESTIONS 

1. Define organic matter. 

2. Distinguish between humus and organic matter. 

3. What is the source of most of the organic matter? 

4. Why are uphmd forest soils low in organic matter? 

5. Where are chernozem soils found? 

G. What kinds of organic matter in soils? 

7. What is a "run-down" farm usually? 

8. Wliat amount of organic matter should soils contain? 

9. What etlect does moisture have on organic-matter content? 

10. Are prairies increasing or decreasing in extent? 

11. How many tons per acre of organic matter in timber soils to a depth 

of (5% inches? 

12. In the subsurface? 

13. Why are soils rich in limestone usually rich in organic matter? 

14. Why do soils of northern latitudes have more organic matter? 

15. Give the changes that organic matter undergoes in the soil. 
10. Which elements increase and which decrease in proportion? 

17. What is the origin of the coal-like materials in soils? 

18. Compare the liun\us of arid and humid regions in nitrogen. 

19. If the nitrogen content of a surface soil is 0.287 per cent, what per cent 

of organic matter does the soil contain? 

20. How many tons per acre? 

21. How is organic matter distributed in the soil strata? 

22. How is the money value of organic matter to be determined? What 

factors are involved? 

23. Of what value is granulation? 

24. \Miat etl'ect does organic matter have on retention of water? How 

many tons of water per acre will an addition of 5 per cent of peat 
enable the surface to hold? 

25. How does organic matter prevent puddling? 

26. How does it aid in correcting it ? 

27. What eftect does it have on temperatTire? How? 
23. How does it affect biological activity? 



ORGANIC CONSTITUENTS OF SOILS 157 

29. How much iiitrogt'ii is required for a 75-buslic'l crop of corn ? For a 

(iO-busliel crop of oatsV For a 40-busliel crop of wheat? 

30. What are the evidences of nitrogen starvation '! 

31. Of what value is organic matter in binding soil particles together? 

32. What part does erosion phiy in loss of organic matter? 

33. Wliat are yellow " clay points " ? 

34. What part does leaching jjlay in loss of organic matter? 

35. tlive an example of loss by lire. 

30. Is nitrification beneficial or detrimental to a soil? 

37. What are the objections to quicklime? 

38. What is meant by fallowing? Give the objects to be accomplished. 

39. What effect does it have on organic matter ? 

40. What was the loss of organic matter due to forest fires ? 

41. Where may fallowing be practiced economically? Why? 

42. What objection to ignition for determining organic matter of soils ? 

43. Describe the dry combustion method. 

44. How may the carbon of soils be determined? 
4.5. Describe the method for determining the humus. 

46. If a soil contains 1.324 per cent of carbon, how many tons per acre of 
organic matter in the plowed soil ? 

REFERENCES 

^Hilgard, E. W., Soils, 190G, p. 130, quoting Kosticheff. 

^Schreiner, O., and Brown, B. E., Bulletin 90, Bureau of Soils, )012', Occur- 
rence and Nature of Carbonized Material in Soils. 

" Hilgard, E. W., Soils, 1900, pp. 130 and 137. 

* Snyder, Harry, Soils and Fertilizers, 1908, p. 105. 

" Soil Reports, Illinois Station. 

"Unpublished data Soil Physics Division, University of Illinois. 

^Snyder, Harry, Soils and Fertilizers, 1908, p. 111. 

'Hall, A. D., The Soil, 1903, p. 109. 

"Wiley, H. W., Principles and Practice of Agricultural Analysis, 1900, vol. 

i, p. 337. 
" Op. Cit., p. 352. 
" Briggs, L. .1., Martin, F. O., and Pearce, J. R., Bulletin 24, Bureau of 

Soils, 1904, p. 34. 
" Wiley, H. W., as above, p. 353. 
"Bulletin 46, Bureau of Chemistry, U. S. D. A., p. 76. 

General Reference. — Alway, F. J., and Bishop, E. S., Jour, of Agr. 
Research, vol. v. No, 20, 1916. 



CHAPTER XII 

MAINTAINING AND INCREASING THE ORGANIC- 
MATTER CONTENT OF SOILS 

The maintaining of the organic matter in soils is the most dif- 
ficult prohlem on the average farm. It, with the nitrogen it con- 
tains, is the limiting factor on most of the farms of the southern 
and eastern states and is fast becoming of primary importance on 
corn and wheat belt farms of the middle west. 

To maintain the organic matter requires something else than 
money. It is not to be had for any price, because there is no 
adequate supply. It must be grown on the farm and put back 
largely as residues which are of low value for any other purpose 
or as manure or both. To maintain this constituent requires very 
careful planning of rotations and the proper handling of the crops 
grown. A few farmers may buy organic matter as grain or hay 
from their neighbors, but this is a very short-sighted policy for 
the latter. The lack of active organic matter is the primary cause 
of soil exhaustion. Many farmers realize its value, but very few 
have made any definite plans for its permanent maintenance. To 
improve a worn-out farm is not an easy task. Since the organic 
matter for our soils must be grown on our farms, the first require- 
ment is that the soil shall be in condition to grow it. Legumes. 
and more especially the clovers, are the best crops to grow for soil 
improvement. They require larger amounts of minerals in the 
soil, especially calcium and phosphorus, than almost any other 
crop. One or botli must usually be supplied. 

1. By Addition of Limestone. — Many soils axe so acid or sour 
that the best soil-renovating crops, the clovers, will not grow suc- 
cessfully. Before these soils can be improved to any extent, imless 
an unlimited supply of manure is available, limestone must- be 
applied. Many experiments have shown that the best form to use 
is ordinary ground or crushed limestone. This neutralizes the 
acid, prevents leaching of organic matter and furnishes the plant 
with the element calcium. 

Limestone is rather readilv soluble. In humid regions from 
500 to 800 pounds are leached out of the soil each year. In many 
158 



MAINTAINING THE ORGANIC MATTER OF SOILS 159 

soils it has been so completely removed that they are acid and the 
element calcium is too deficient to produce good crops, especially 
of legumes. Applications should be made once in every rotation. 
To maintain the limestone at present prices costs from fifty cents 
to one dollar per acre per annum plus the cost of applying it. 
This will make possible the growing of legumes for soil-renovating 
purposes. On eroded hill land large growths of sweet clover 
amounting to 2.7 tons per acre for the two years of its growth 




Fig 80 —Clover on gray silt loam on tight clay. (Marion silt loam.) Manure gave 
0.6 ton of grass with practically no clover, while manure with rock phosphate and Umestone 
gave 2.65 tons of good clean clover hay. (Illinois Station.) 

were made possible by the application of four tons of limestone 
to acid soil. 

2. By Applications of Phosphorus. — Phosphorus should be 
mentioned in this connection because so many soils are deficient in 
this element, and its application is very necessary for increasing 
the growth of legumes. It often more than doubles the growth of 
clovers and, of course, gives a larger amount of much-needed active 
material to be turned under. The acids formed in the decay of 
organic matter aid greatly in the liberation of phosphorus and 
potassium that are locked up in the minerals in the soil. The 
average increase of cloveT at the Illinois Station at Urbana on 
brown silt loam was 1.05 tons per acre where phosphorus was used, 
while on another field on the same type the increase was 1.51 tons. 



160 SOIL PHYSICS AND MANAGEMENT 

At Fairfield, in southern Illinois, on gray silt loam on tight clay, 
Marion silt loam, the gain for phosphorus, limestone and manure 
ovei manure alone was 3.65 tons per acre of good clover hay. All 
know that the growing of large legume crops aid the production of 
large crops of grain (Fig. 80). 

3. By Accumulations in Pastures. — The livestock farmer has 
one decided advantage over the grain farmer in that some of his 
land must be in pasture and accumulations of organic material 
are taking place during this period of " rest." A large amount of 
the organic matter that grows in the pasture will be eaten and de- 
stroyed by stock in the process of digestion, but the total result 
will be beneficial to the soil. Fl"om the table on page 162 it vsall 
be seen that only 580 pounds of organic matter are recovered in 
the manure for each ton of pasture grass eaten by stock. For red 
clover pasture, the amount is, 680 pounds, while for alfalfa it is 660 
pounds. Pasture grasses develop systems of roots which add quite 
largely to the organic supply in the soil. If legumes can be grown 
in connection with these,, pasture gi'asses much better results will be 
secured than from the grass alone. In the case of sweet clover 
growing with blue grass, it is found that the amount of blue grass 
will be larger than if grown alone. In pastures there is very little 
organic matter lost by oxidation, since this process is not very act- 
ive in sod, there being no more nitrates formed than are used by 
the grass.. In old compacted pastures, nitrification is not sufficiently 
rapid to maintain a good growth of grass. Farmers speak of such 
pastures as being " sod bound." Plowing and reseeding or at 
least a thorough disking may be necessary to completely aerate 
the soil and bring about larger growth. 

Pasture grasses are frequently eaten so closely by stock that 
very little benefit is derived by the soil. Clover is often pastured 
so that at the end of the season there is nothing left on the ground 
to turn under for soil improvement. 

4. Green Manures. — One of the very important ways of in- 
creasing the organic matter is by the use of green manures. Almost 
any crop may be used for this purpose, but legumes are much better 
because of the greater value of the material for soil improvement. 
The crop selected should depend upon the time of planting, the 
period available for growth, the character of the soil to be im- 
proved, and the system of farming practiced. The legumes best 
adapted to single summer growth are cowpeas, soybeans, common 
vetch, field peas, and velvet beans. Eed, sweet and mammoth 



MAINTAINING THE ORGANIC MATTER OF SOILS 161 

clovers are biennials and can be seeded one year with a nurse crop 
and allowed to produce a growth the next spring before turning 
under. Hairy or winter vetch may be seeded with rye or winter 
oats for early spring pasture and plowed under for corn, cotton or 
other crops. It is a common practice in the corn belt to sow clover 
with wheat, oats or rye and turn it under in the fall or the fol- 
lowing spring for corn. Sweet clover is excellent for this purpose 
in many localities. One to two tons of dry material have been 
turned under in time for the corn crop without apparent injury. 
There is danger, however, from plowing under a large amount of 
green material to be followed by a crop of corn, cotton, or potatoes. 
During the last few years some complete failures have resulted from 
this practice. The green crop takes out much of the available 
plant food and moisture and may leave the soil so deficient in these 
that the crop which follows may be seriously injured. Besides, the 
fermentation of the green material may develop heat that will drive 
off some moisture and leave the soil still drier, although the large 
amount of water turned under with the green crop would tend to 
compensate for any lost in this way. 

• 5. Catch and Cover Crops. — Many times it is advantageous 
to use crops for some special purpose in which no attempt is made 
to grow them to maturity. Legumes, rye, oats or other crops are 
sometimes sown on land that is to lie idle for a time in order to use 
the available nitrates and prevent their loss by leaching. This 
plan is especially advisable on sandy soils, but it may be applied 
to other soils to good advantage. Wheat on sandy land could be 
immediately followed by cowpeas, which not only conserve the 
nitrates but add nitrogen to the soil. Wheat and oats on heavier 
soils, such as silt and clay loams, are usually followed soon after 
harvest by a crop of weeds and grass which act as very efficient 
catch crops. Wherever possible legumes should be grown after 
oats, wheat, or barley for this purpose because of their double value. 
Covrpeas, soybeans or clover are sometimes seeded in corn at the 
last cultivation to be used as a soil-improving catch crop. They 
may also be seeded in the hill of corn without serious detriment 
to the corn. Eape, cowhorn turnips, or rye may be used as catch 
crops. These may be pastured and thus acquire an additional 
value. 

The same crops may be used as cover crops in orchards to 
hasten the maturity of wood or on hillsides to prevent washing. 

6. Barnyard Manures. — Manure is one of the most valuable 
11 



162 



SOIL PHYSICS AND MANAGEMENT 



by-products of the farm; however, sufficient manure cannot be 
produced from the crops grown on tlie farm to maintain the supply 
of organic matter. Tliis is due to the fact tliat a large amount of 
the organic matter is destroyed during the process of digestion. 

Average Digestibility of Some Common Feeds ^ 



Feeds 




Dry matter recovered 
in manure 



Pasture grasses 

Red clover, green. . , 

Alfalfa, green 

Mixed meadow hay 

Red clover hay 

Alfalfa hay. 

Oat straw 

Wheat straw 

Ck)rn stover 

Shock corn 

Corn-and-cob meal. 

Corn ensilage 

Oats 

Corn 

Wheat bran 



powids -per ton 

580 

680 

660 

780 

780 

800 
1040 
1140 

800 

740 

420 

720 

600 

180 

780 



From the above table it is seen that in feeding hay about 40 per 
cent of the organic matter, or 800 pounds per ton of hay fed, is 
recovered in the manure, while with pasture grasses an average of 
32 per cent, or 640 pounds per ton, is recovered. In the feeding of 
straw, shock corn or even ensilage, the animals leave a considerable 
amount, so that somewhat more organic matter is recovered than 
indicated by the figures. 

The amount and composition of manure produced by different 
animals vary quite widely. The following table gives the amount: 

Amount and Value of Manure, Solid and Ldquid, Excreted by Various Farm 
Animals per 1000 Pounds of Ldve Weight 



Animal 


Pounds 2 
per day 


Average 2 
tons per year 


Per cent ' 
solid 


Per cent 3 
liquid 


Value 2 


Horse 

Cow 


35-45 
70-80 
40-50 
40-50 
30-40 


7.0 

12.7 

7.5 

7.3 

5.5 


80 
70 
70 
60 
67 


20 "^ 

30 

30 

40 

33 


S19.88 
28.07 


Steer 


21.75 


Swine 


25.48 


Sheep 


32.06 







In connection with this, attention is called to the next table, 
which gives the composition of the manure : 



MAINTAINING THE ORGANIC MATTER OF SOILS 163 

Composition of Fresh Manure * 



Animal 


Excrement 


Water 


Nitrogen 


Phosphorus 


Potassium 


Horse 


per cent 

Solid 80 
Liquid 20 
Mixed . . 


per cent 

75 
90 

78 


per cent 

.55 

1.35 

.70 


per cent 

.13 

Trace 

.11 


per cent 

.33 

1.03 

.45 


Cow 


Solid 70 
Liquid 30 
Mixed . . 


85 
92 
86 


.40 

1.00 

.60 


.09 

Trace 

.07 


.08 
1.11 
.37 


Swine 


Solid 60 
Liquid 40 
Mixed . . 


SO 
97 

87 


.55 
.40 
.50 


.22 
.05 
.15 


.33 
.37 
.37 


Sheep 


S9lid 67 
Liquid 33 
Mixed . . 


60 
85 
68 


.75 

1.35 

.95 


.22 
.02 
.15 


.37 

1.74 
.83 



7. Loss of Manure and its Prevention. — A source of great 
loss occurs in the handling of manure after it is produced. In too 
many cases it is left in the lot or under the eaves of the barn 
or shed until the prganic matter is decomposed and a large amount 
of the fertility is carried away. In the process of rotting there is a 
large amount of organic matter lost. To determine the amount 
of loss the Ontario Station placed four tons of mixed cow and 
horse manure in equal amounts in a protected shed and a like 
amount in an open bin exposed to. the weather. The four tons 
contained 1938 pounds of organic matter. The losses are given 
in the next table. 



Loss cf Organic Matter and Fertility in the Rotting of Manure ^ 



Fresh 



Weight of manure 
Weight of organic 
matter 



Pro- 
tected 



Ex- 
posed 



pounds 



8000 
1938 



8000 
1938 



A-t the end of 
three months 



Pro- 
tected 



Ex- 
posed 



pounds 

2980 3903 
791 



At the end of 
six months 



Pro- Ex- 
tected posed 



pounds 



2308 
803 



4124 
652 



\i the end of 
nine months 



Pro- Ex- 
tected posed 



pounds 

2224 4189 
760 648 



At the end of 
twelve 
months 



Pro- 
tected 



Ex- 
posed 



pounds 

2158 3838 
770 607 



Loss in per cent 



Organic matter 

Nitrogen 

Phosphorus . . . . 
Potassium 



55 


60 


58 


65 


60 


67 


60 


17 


29 


19 


30 


23 


40 


23 


None 


3.5 


None 


5.2 


None 


5.7 


1.7 


None 


16 


2 


21 


2 


24 


2 



69 
40 

7 
25 



164 ' SOIL PHYSICS AND MANAGEMENT 

It is very impoTtant that the manure should be handled in such 
a way as to lose as little as possible. The best plan is to scatter 
it on the land as . soon as j)racticable after it is produced. If the 
fertility is leached out then it goes into the soil, and if the manure 
becomes dry there is essentially no loss. The farm should be man- 
aged, if possible, so there would always be a place to haul manure. 
If this is not feasible under the system followed or if the fields be- 
come too wet to draw the manure upon them, the problem of pre- 
venting loss becomes an important one. It is well to remember 
that the greatest losses are due to fermentation and leaching. 

(a) Fermentation. — The process of fermentation is largely re- 
sponsible for loss of nitrogen and organic matter. It is practically 
impossible to prevent it entirely, but it should be reduced to a 
minimum. When manure, particularly from horses, is thrown into 
a pile it soon begins to heat. This indicates that bacterial action 
or fermentation is taking place. The organic matter of the manure 
is being decomposed and nitrogen in the form of ammonia is given 
off, resulting in large losses. In connection with this process, 
other organisms may work, causing "fire fanging," resulting in 
a light, powdery form of manure of little value. A process of 
fermentation takes place in cow manure or compact manures that 
results in rotting without so much loss. This is known as putre- 
faction and is due to anaerobic bacteria or those working without 
oxygen. The fermentation may be largely prevented by excluding 
the air, since oxygen is necessary for the process. This may be done 
in two ways, first by allowing stock to trample the manure, thus 
compacting it so much as to exclude the air, and, second, keeping 
the manure very wet. 

(b) Leaching. — The greatest loss of manure is due to leaching, 
as it affects all constituents and elements alike. The colored liquid 
draining from the manure heap carries large amounts of valuable 
material away in the drainage waters. The Ohio Station fomid 
that manure from steers exposed for three months, January to 
April, decreased in plant food value per ton from $3.01 to $1.85, or 
there was a loss of $1.16, or 38.6 per cent. The loss of organic 
matter was fully. as great. Leaching may be prevented by keeping 
the manure in a shed to protect it from the rain. If exposed, it 
should be kept in a concrete pit or tank to prevent loss by leaching 
and very wet to prevent heating. Horse manure is the most diffi- 
cult to keep because of its tendency to heat, owing to its looseness 



MAINTAINING THE ORGANIC MATTER OF SOILS 165 



and the free access of air. Where possible it should be mixed with 
cow inauure to render it more compact. 

If the animals are being fed in a shed or barn where the manure 
may be left till it is hauled out there will be less loss than in any 
other way. If a cement floor is used there will be no loss by leach- 
ing and the tramping of stock will exclude the air so that very little 

Fig. 81. 




Fig. 81. — How does this man handle manure? The stains answer the question. 
Fig. 82. — When the spreader is filled the manure is hauled to the field. In this way there 

is very little loss. 

fermentation will take place. Various experiment stations have 
demonstrated the higher value of manure and the lower loss when 
kept in this way. Compare figures 81 and 8'2. 

(c) Absorb ents. — Substajices that act as absorbents of ammonia 
and other constituents that would be removed easily are sometimes 
mixed with the manure. Dry earth or dry peat may be used to 



166 



SOIL PHYSICS AND MANAGEMENT 



good advantage. Calcium sulfate, land plaster, may be dusted 
over the manure. The sulfuric acid unites with the ammonia, 
forming ammonium sulfate, which is comparatively slowly solul^le. 
Common salt is sometimes used, but both it and land plaster are too 
expensive for general use. 

Certain substances may be used as absorbents and also for re- 
enforcing the manure. If the manure is to be used on land de- 
ficient in the element potassium, kainit may be used for this pur- 
pose and when the manure is. scattered over the land will supply the 
needed element. Finely ground rock- phosphate or floats may be 
used as an absorbent and at the same time supply the element phos- 
phorus, in which most soils are deficient. At the Ohio Station the 
average annual increase for stall manure and floats over stall manure 
alone was 7.2 bushels of corn per acre, while the increase for yard 
manure treated over untreated was 6.4 bushels. The corresponding 
increases for wheat were -i.l and 3.4 bushels per acre. 

The next table shows the amount of loss from manure with 
absorbent reenforcement exposed for three months. The experi- 
ments were made at the Ohio Station. 



Composition of Steer Manure After Exposure for Three Months — Pounds 

Per Ton ^ 



Treatment 



Floats = Rock 
phosphate 

Acid phosphate 



Kainit 



Gypsum 



Untreated 



Pounds at beginning 
Pounds at end 
Per cent of loss 

Pounds at beginning 
Pounds at end 
Per cent of loss 

Pounds at beginning 
Pounds at end 
Per cent of loss 

Pounds at beginning 
Pounds at end 
Per cent of loss 

Pounds at beginning 
Pounds at end 
Per cent of loss 



Organic 
matter 



349.00 

310.74 

10.96 

357.80 

269.89 

24.57 

369.00 

291. .50 

21.00 

375.40 
267.35 

28.78 

416.00 

254.79 

38.75 



Ash 



120.20 
98.95 
17.67 

101.40 

85.88 
15.30 

107.40 
83.64 
22.12 

104.60 
75.72 
27.61 

79.20 
65.68 
17.07 



Nitro- 
gen 



10.70 

7.46 

30.28 

9.86 
7.18 

27.18 

9.76 

6.68 

31.56 

9.68 

7.94 

17.97 

10.30 

7.18 
30.29 



Phos- Potas- 
phorus slum 



7.38 

3.52 

52.30 



8.60 

7.57 

11.97 

5.70 

4.79 

15.96 

2.88 

2.48 

13.89 

2.76 
2.66 
3.63 

3.24 

2.47 

23.76 



6.88 

2.99 

56.54 

10.70 

4.98 

53.46 

7.86 

2.56 

67.42 

8.14 
3.35 

58.84 



The value of manure in a soil depends upon three things : 
first, the beneficial physical effect produced ;' second, the plant food 
supplied, and, third, the stimulus given to bacterial activity. Its 



MAINTAINING THE ORGANIC MATTER OF SOILS 167 

real value to the farmer can be determined only by the money 
returns secured from increased yields. This depends upon several 
factors : the soil itself, the crop grown, the price received for the 
crop, the rate of application and the cost of the manure. 

As a general rule the better the soil the less need there is for 
manure and the smaller the returns per ton from its use. The 
poorer the soil the greater the need and the larger the returns. 
Farmers recognize this fact and usually apply manure to the poorer 
places on their farms. 

All crops do not respond equally well to manure. Its value 
may be increased by applying to the right crop. Timothy, corn 
and wheat usually give good returns from applications of manure, 




Fig. 83. — Manure spreader in action. The manure i^ torn ipart so as to be scattered uni- 
formly. (J. C. Beavers, Cir. 49 Purdue Station.) 

yet corn may be a complete failure after manure. This is not 
usually the fault of the manure, but of the amount applied and 
subsequent management. Strawy manure plowed under late in 
the spring without disking is- very likely to injure corn because of 
the effect on moisture movement. 

The common impression is that heavy applications of manure 
are most profitable. The greatest profit per ton of manure is ob- 
tained from light applications when well distributed. This may 
best be accomplished with the manure spreader. At the Ohio Sta- 
tion at Wooster an average of twenty 3^ears shows a value of $3.48 
per ton where four tons of manure were applied, $3.70 with 8 tons 
and $2.34 with 16 tons per acre. 



168 



t^cUL niYSlCS AND MANAGEMENT 



'IMio I'ollnwiuo- table g-ivos data t'roiw riirduo Siatiou aiul illus- 
trau\< the value of ditVereur aniounrs: 

Ammge Value of Incnase for Manure Per Crop ami Per Ton for Twcntij-three 

Years, 1890-191:^' 



Rotations 



Average amount in 
tons per rotation 



Com 

Oats 

Wheat 

Clover 

Average i>er ton of manure 

Corn 

Oati; 

Wheat 

Aveniiie ptn- ton of n\anui-e 

Corn.: 

Wheat 

Average per ton of manure 

Corn I'ontinuously 

A\erage ^vr ton of manure 

A\ heat eontinuovislv 

Average jxm- ton of manure 

Average ^hm- ton of manure for all i 
experunents 



heavy \ 

14.24 



15.00 

i6!d4 



light 

8.8 



9.1 

6^72 
3.S1 

9 7-^ 



Value of increase 



heavy 


light 


$3.11 


$3.78 


4.7S 


4.03 


5.S3 


4.52 


4.91 


3.90 


1.31 


1.84 


8.55 


6.68 


4.9S 


4.28 


7.33 


5.53 


1.39 


1.81 


8.16 


6.81 


11.45 


9.33 


1.79 


2.40 


6.79 


6.38 


1.02 


1.67 


6.17 


5.25 


1.42 


1.93 


1.39 


1.93 



{d) Jdeihoih' of Applt/ini) Manure. — For an application of 
mainire to be most effective it should be eveuly distributed atul 
then thoroughly mixed with the soil. It is very difficult to accom- 
plish the tirst by hand spreading. There will almost certainly be 
large clmnks of manure alternating with bare spots. The manure 
spreader (Fig. So) is indispensible for this purpose. It tears tJie 
maiitire to pieces, scatters it evenly and permits of smaller applica- 
tions. The same amount of manure covers a larger area and. as 
seen from the above table, gives it a higher value per ton. The 
mixing of the manure with the soil may be readily accomplished 
by the disk. This is not so important unless a crop is to follow 
soon, as in the ease of spring plo^^•ing for corn or summer plowing 
for wheat. It is especially desirable for coarse manures which when 
plowed under interfere with capillary movement. 

The mantire should be applied as soon as possible after being 
produced, since there is less loss when in or on the soil than if left 
in the lot or even the shed (Fig. 8*^). Some farmers prefer well 
rotted manure, but there is too much loss in the process of decay to 
allow this to go on in any other place than in the soil. Weight for 



MAINTAINING THE ORGANIC MATTER OF SOILS 169 

# 

wciglil, well rotted manure may be Jiioi'e valuable than fresh 

manure, but tbe loss ot fertility and organic matter involved iji the 
process more than overbalances the benelits. The character of the 
rolled manure will depend upon the conditions under which the 
decay took place. '^^I'liere is no question l)ut that twenty tons of 
fresh manure applied to soil will produce fi^rcater increase than 
the same weight of manure would after it is well rotted. In many 
cases it is not practical to apply manure as rapidly as produced. 
Farmers of the corn belt haul out the manure in summer and 
early spring. That taken out in summer is usually placed on land 
to bo fall plowed. This is without (lon1)t a good practice. The 
manure becomes decayed sulhciently by spring so that it will not 




Fig. 84.— An 



uud wasU.lul way of handling manure on the farm. 
it in piles. (Deere & Co.) 



Do not put 



interfere with moisture movement. The fall and winter loss is 
avoided. 

Coarse manure is best applied in the fall, but if the apj)lica- 
tion is made in spring it should be very light. Heavy spring appli- 
cations may ruin the crop, especially corn. In the dry summer of 
1914 corn on some fields that had received heavy applications of 
manure before being ])lowed in the spring produced no grain 
whatever. 

Manure is sometimes piled in the field in small heaps and later 
scattered with the fork. This is not only an expensive but a 
wasteful process. Much of the fertility is leached into the soil 
beneath the heaps and a large amount of manure is left at these 
spots in spreading (Fig. 84). The result is a great many very 
rich spots upon which small grain lodges badly and is frequently 



170 



SOIL PHYSICS AND MANAGEMENT 



lost. Those spots aiv still visible h\ oats after .'5 years on a rami 
in the vicinity of the University of llliuois. 

8. Organic Residues of the farm are of two kinds, those that 
form no part of the crop, as weeds, and those that are part of the 
crop or harvested with the crop, such as corn stalks, straw and 
stubble. Heretofore it has been believed by many farmers that 
most crop residues have little or no value and the easiest way of 
disposing- of them was the best : consequently much material wa= 
burned and the practice has by no means ceased. It is estimated 




Fio. So. — Burning corn stalks — In addition to the organic matter destroyed in burning the 
stalks some organic matter in the soil is burned. 

that in the western part of the United States the straw from •^0.000,- 
000 to 30.000,000 acres of grain is burned every year, while in the 
corn belt the practice of burning stalks is still somewhat prevalent in 
certain sections (Fig. 85). This enormous waste of organic mat- 
ter and nitrogen is to be regretted very much. Crop residues of 
all kinds have great value. Chemists tell us that straw has a 
manurial value of $*? to $3 per ton, over half of which is due to 
the plant food which it contains, while the rest is due to the physical 
effect upon the soil. Corn stalks contain 16 pounds of nitrogen per 
ton, and even after exposure during the winter the amount is re- 



MAINTAINING THE ORGANIC MATTER OF SOILS 171 

duced only about ly^ pounds, so that the ))uniing of corn stalks 
results in a loss of 1-iVii pounds of nitrogen per ton, which at 15 
cents a pound would amount to $2.17. There is little doubt but 
that the value of the corn stalks for improving the tilth would be 
equal to one-half of the value of the nitrogen, so that for turning 
back into the soil the corn stalks are worth fully $3 per ton. The 
value of residues is shown in the yields secured where they have 
been returned to the soil for a number of years. 

One of the most valuable crop residues is that from legumes, 
which are frequently grown for the seed and the .straw returned 
to the soil. It furnishes organic matter in its most active form, 
rich in nitrogen, and its rapid decomposition makes it one of the 
best amendments for soils in bad physical condition. 

On the experiment field at Bloomington, Illinois, where crop 
residues had been turned under for five years, the yield of wheat 
for 1911 was increased 4.4 bushels over that where the crop residues 
had been removed, and in 1912 the yield of corn was increased 7.9 
bushels and in 191.3, 5.9 bushels. At the experiment field at Du Bois, 
Illinois, crop residues turned under gave an increase of $19.38 * 
for twelve crops, or $1.61 per acre annually, while with phos- 
phorus applied the increase for residues was $40 for the twelve 
crops, or $3.33 per acre. 

The turning under of crop residues on the grain farm in the 
corn belt is very essential, since it is the only means the grain 
farmer has of maintaining the organic matter. If he makes use of 
residues and an occasional crop of clover he has even a better 
chance of maintaining the organic matter than the stock farmer 
who loses so much organic matter during the process of feeding. 
(See the table page 162.) 

9. Growing Non-Tilled Crops. — Tillage increases oxidation of 
organic matter by bringing about favorable conditions of moisture 
and aeration. The compact condition of the soil where non-tilled 
crops are grown retards decomposition of organic matter, hence 
the benefit of such crops as wheat, oats, rye, barley and grasses. 

10. Rotation of Crops. — Rotation permits the growing of tilled, 
non-tilled and soil-renovating crops. Farmers should plan their 
rotations with the thought of soil maintenance. This is funda- 
mental. The lengtli of the rotation and crops selected should be 
adapted to the soil and to the system of farming. On soils well 

*The price of corn was figured at 3.5 cents per bushel, oats at 30 cents, 
wheat at 70 cents, cloverseed at $0 and soybeans at .$1 per liushel. 



172 



SOIL rilYSlCS AND MANAGEMENT 



suppliod with organic uuuior the nnation .should bo quite dilVorout 
from that on !?oiU ilolicioiit in tliis eonstituent. In the I'ormer 
ease luueh of tlie residue!? might be sokl from the farm, while in 
the latter uuieh the larger part should be returned to the soil. One 
essential of a rotation for soil im]irovoment is at least one legume 
erop during the CYole. Soils detieient in organic matter should 
have a more frequent recurrence of this crop, as the value of the 
rotation in improving the soil depends primarily on the use of it. 
The legume should be turned hack into the soil whenever possible. 
If it is removed and nothing returned in its ]>lace very little or 
nothing is gained for permaneui soil improvement and maintenance. 




Fio 



Adiing organic mauer to the soil in the fornt of sweet clover. 



Clover and co\vpeas are commonly grown. The best one to grow 
on the grain farm is that which provides the largest amoimt of 
material to turn under. ^Medium red clover is most common in the 
northern states, but alsike or sweet clover is better adapted to 
somewhat poorly drained soils. Manunoth or English and sweet 
clover probably furnish the largest amount of material to plow 
imder, and both plants will furnish a fair crop of seed, upon which 
the farmer must depend for his immediate returns. It requires 
the very best conditions for red clover to produce three tons per 
acre for both crops, which is at least one ton above the average. 
SAveet clover is an excellent legume for soil improvement because of 
its large growth (Fig. 8(0 and deep rooting characteristics. 



MAINTAINING THE ORGANIC MATTER OF SOILS 173 



The following table gives the amount that lias been produced 
during the two years' growth : 

Investigation of Sweet Clover {Melilotus alba)^ 





Depth 
(inches) 


Dry matter per acre 


Nitrogen 


per acre 


Parta of plant 


Pounds 


Per cent 
of total 


Pounds 


Per cent 
of total 


Total tops 




10367 

1809 
601 


81 

14 
5 

19 

100 


197 

22 
9 

31 

228 


86 


Total surface roots 

Subsurface roots 


Oto 7 
7 to 20 

Oto 20 


10 
4 






Total roots 


2410 

12777 


14 


Total tops and roots . 


100 



From the above table it will he seen that the sweet clover pro- 
duced G.-i tons of total dry matter. Of this 1.2 tons came from 
the roots. The total weight of sweet clover from a single year's 
growth in the dry season of 1914 on hlack clay loam was 4.4 tons 
per acre. 

QUESTIONS 

1. Would it be advisable to purchase manure for ordinary crops? 

2. What is the first requirement in maintaining organic matter? 

3. Why is it necessary to add limestone? 

4. What is the cost of maintaining it? 

5. What is the effect of phosphorus on growth of clovers? 

G. What advantage does the livestock farmer have over the grain farmer ? 

7. How much organic matter is lost in the process of digestion of pasture 

grasses? Of alfalfa? 

8. What is the remedy for " sod bound " pastures? 

9. Why is pasturing often of little benefit to soil's? 

10. What points should be considered in selecting a crop for green manure? 

11. Give danger to crop arising from green manure turned under in spring. 

12. What are catch crops? For what used? 

13. Explain under what conditions weeds may have some value. 

14. What is the use of cover crops? 

15. In pasturing red clover what per cent of the organic matter is lost? 

16. What proportion of the corn fed is recovered in the manure? 

17. If a farmer keeps 10 horses averaging 1400 pounds each, .5 cows of 

800 pounds and 10 hogs of 100 pounds each, what is the value of the 
manure produced in a year ? 

18. What are the sources of loss of manure? 

19. Give the experiment condxicted l)y the Ontario Station. 

20. Why is there no loss from dry manure? 

21. What is " iire fanging "? 
22'. What is putrefaction ? 

23. How may fermentation be prevented? 

24. What jiarts of manure are affected by fermentation? 



17 1 8011 rinSlOS ANP MANA».U\lKNr 

iti. \Vh»t \V!»j^ viott^nuuu\l \u xv^^nl tv> lo^^s^ fnuu iimimiv bv tho Ohio 

, St*t tvvn t 
iT, Whst is tht» lH\st WHY tv^ kwp manun^ to jnwtMU U»**? 

il>. \VU»t »rt^ tUo «*<v of wt^iit'oiviiViJ mstevial?*? 

50. V'jHVU wlvHt dvH"^ tlU> V»hlO vU' niHUUlV vlt^^HMUlt 

51, "lUnv lUsSy it!ii n\>l vahvo W dotormiiuslT I ^hmv vvlvut vUhv* thi* dejvnd? 
Si. On whAt kiuvl v^f svvil s-hvUiUi »«si\\uv W api^Utnl? 

SS. \\h«t oivps iv?ijv»Kl lv«it to m.-iiuuv? 

54, Whst awoimt* ot' mnyuuv aiv Ivj^t to Apply t 
So. «.»i\o tho w^uUji ol>ta»nt\l bv tho l^u^luo St«tio«, 

SO. \Vh*t aiv tho advHtvtA^vs to Iv gsuiuxl by tho t»*t> of tht> lUAUUiv 

ST. WhsHt i# tho vaIuo of vvnt *tslV,s aikI siiniwr 

55, Wh*t iuotvAso* hsvo Kvn obtsiutxl by tho «so of otvp nNjaduos? 
Si>. Whst is tho s»dvHtvt;>^x^ of sjivwiu^- «o«tilU\l orv»p** 

40, Whst is os:^nvti«i in .s vv^tstioix for sos^ in^piwomont* 

41. How shvmUl tho lojjnnio Iv n»j»»».-<g\sl? 

4i. \\ hioh h\s;untiN#^ aiv InNi^t tor soil impnnoinont * 

4S. What vv.Hs tho total an>ount of oi-ji5»nio n»«tt«>r juxhUioxxI by a sin^5»lo 
s^x-isou's i^ivwth of swtvt olovor? 

REFEKKNCKS 

*>loj^iwss C» Ov, Stwl »ttiUty and IVrtnatunit .VsriowUuiv. 1910. iv 301. 

* Ih^vovs. »1. 0.. CiToulai^ 49.* l\u\l«o Ststion. F»rm ManutViS, 1915, jv S. 
*\an 8lNko. U U. >VrtiU«or* and S^viK lOKn p. 391. 

*0i\ at,. V, i*.n. 

* Ontario Station. 

* rhv>vno. l\ K,. Farm Nlanur*^. 1914. p, 14S. 
^ Ciivular 49, Ihmluo Station. |V 14. 

* Uoi^kins. C. U., Soil Mortality ami IVnuanont -V*»^*l^«'^'- ^^'^^^^ l^- -^^- 



('iiAi"ri';i:, xiii 



j>iiYsiCAL jmijoim<:rtij<:s oi^ soils 

1. Real or Absolute Si)ccific Gravity. 'I'lic rcjil i |»((](i(; 
;^'riivil,_y of hoi'Ih viiricH willi IIh' knid ;iii<l jiiioiinl of hiimitjiIs coin 
|)0Hiii;4' lliciii Mild (lie jiiiumiiiI, of ()r;';iiiic iii;iI1im' picsciil. 'I'Ik; 
Kpccinc /.n'iivily (tf ,sMiiic of I lie more inipoiliinl, imncriilH in kojIh ih 
^'ivcii ill llii' rollou'iij;^ liihlc: 

tSpec'iJu: f/rdiiil!/ iif H(yi,l^Forfn,l;n,ii Mi.urrtdH 



Quart/. 

Albito 

()rl-li()cliiH(!. 
( )li>z;()(;ln,H(!. . 
Jjiihriuloritf! 
Aiiortliilc, . 
Doloinilj;. . . 
l>iiMi)tiil(;. . . 
MiiKiuititu. . 
Z(!()lit(!H. . . ■ 



2M 
2f,\ 
2.r,i'> 
'2m 

'2.7'^ 

2.Hr) 
:{.« to 4.0 

CO to 5.1 
2.25 



Kiioliiiiti;. 
Aiiij)liil)(>l( 
i*yrox(!/i(!, 
Mimcovitc 
iJiotiti!. . . 
CiJdtf!,. , 
( lyi)Hiiiri, . 
i l(;tiiiilit(;. 



2.r>{) 
2M to AA 
:',.2 to :i.5 
2.7 to ;i.o 
2 7 to:'.. I 

2.70 

2:m 

4.5 to 5.:i 

:j.25 to ;j.5 



()r^;iiii<Miiiil Icr is llic li^^lilcsl soil coiistil iicnl, ils spccidc |vr;i,vi'ly 
iKiiii;.^ \wi to l.;i. 'I'Ik; H))(!c.i(i<; /.^ruvily of llic wiirrucc soil of brown 
KJIt lojuii, ili(! coninion priiii'ic! soil of I.Ik! corn IksII,, is 2.(')2, of [^Tiiy, 
ycillow i^f'ty, or yellow sill, lonni 'iJ'>r>, wliilo of bliick chiy loiuii il, 
iH 2.n7. 

2. Apparent Specific Gravity. The renl specific ;^;riivily is of 
vory liill(( imporiuiKu^ in eoinpiirison willi Hie iippni-enl specific 
f^niviiy, wliieli is ilu; riiJ io l)<-l,we('ii the witi^^lil, of ;i, iiiiit volume 
of wilier free soil mid the siiiiie voIiiiih! (d' Wiiler. TIh; exprcission, 
voliinK! wifi^iii, is soni(!t,ini(!H upjilied l.o iliis and niprescftilH IIk; 
wei;.^iii of Ji uiiii volume of soil. The iippareni speeifie gravity is 
nurn(!ri(;ally similler tlinii Ihe reiil specille /^rnviiy hecaiisf;, in Hie 
latter, tiio pore 'Sp;ie(; is climimilerl. The iippiireid, specific Mrnvify 
varies direclly ns Ihe kind iiiid iiiiioiinl of miiicriils iiiid Ihe com 
piieltiess, and inversely iis I hi' iimoiinl, of orf^anie inailcr pniseiii 
iiiid ili(i porosily of Ihe soil. II, is ohiiiined hy dividin/^'- Hk; w<!i;.;ht 
of a e((riain volume of soil \iy I Ik; wei<^hl, of IIh; sjime voIiiiik! of 
water, or, what amoiinis Jo IIk; same; lliin^', tlie weij^hl of Ihe soil 
in ^M-aniH hy ihe volume of ihe Koil.iii euhie e(;nL)iiiet(!rK. 

175 



176 SOIL PHYSICS AND MANAGEMENT 

Under different systems of tillage of the same soil type, the 
apparent specific gravity is an approximate measure of the tilth 
of the soil when determined under field conditions. In order to 
do this take a tube with a cutting edge and force it into the soil 
to a certain depth marked on the tube, thus securing a definite 
volume of the soil. Dry, weigh, and compare with an equal volume 
of water, or, in other words, determine its apparent specific gravity. 
The soil having the lowest apparent specific gravity is in best tilth. 
As an illustration, the apparent specific gravity of brown silt loam 
from a heavily cropped field was 1.36, while that of a well treated 
field was 1.10, indicating that the latter was in much better tilth 
than the former. The apparent specific gravity of soils varies from 
1.7, that of sand, to 0.5, that of peat. 

3. Weight of the Soil. — The weight of any quantity of soil 
may be determined by multiplying the weight of an equal volume 
of water by the apparent specific gravity of the soil. A cubic foot 
of soil varies from 106 pounds to 31 pounds per cubic foot, the 
former being sand, the latter peat. Knowing the weight of an 
acre-inch of water to be 226,000 pounds, it is easy to obtain the 
weight of an acre-inch or any number of acre-inches of soil. (See 
the table page 120 for weight of soil strata.) 

• 4. Color of Soils. — The color of soils is one of the most notice- 
able or striking characteristics and always appeals to practical 
farmers as one of the best means for indicating soil differences. 
Its importance in estimating the character of the soil must depend 
upon the material producing it. Color is due almost entirely to 
the presence of two substances, organic matter and iron in some 
form. 

The color imparted by organic matter varies with the amount 
present, the stage of its humification, the moisture content of the 
soil, and the amount of limestone present. The color imparted 
varies from black through brown to gray. The least decomposed 
imparts a brownish color, while the organic matter that is thor- 
oughly himiified gives a very dark brown or black color to the soil. 

The presence of limestone imparts a darker color to the organic 
matter and hence to the soil. It further aids by preventing the 
leaching out of the black humus by forming insoluble compounds 
with it. Soils fairly well drained but deficient in limestone are 
usually light in color. The acid of soils bleaches the organic matter 
so that its effect in coloring soils is not so striking as in those 
containing limestone. In areas of acid soils, the presence of lime- 



PHYSICAL PROPERTIES OF SOILS 177 

stone outcrops are indicated by dark soils. Coffey ^ speaks of being 
able to trace an outcropping limestone stratum by the dark color 
of the soil, and the same thing has been observed in the southern 
part of Illinois in the acid soils of that region. In soils of arid 
regions limestone is frequently so abundant as to impart a light 
color. 

Iron oxides give various colors to the 'soil, depending upon the 
degree of oxidation. Ferric oxide (FeaOg) imparts a bright reddish 
color. Due to the presence of this oxide, many of the subsoils of the 
Piedmont Plateau are decidedly red in color. The hydrated ferric 
oxide (2Feo03.3H20) imparts a dull yellowish color to the soil, but 
is 'Sometimes mixed with the anhydrous ferric oxide, giving a red- 
dish yellow or yellowish red color, depending upon which predomi- 
nates. In some cases, deoxidation has occurred through the effect 
of organic acids, or some other agency, and the higher oxides of 
iron have be6n reduced to the lower form. This gives a bluish, 
grayish or drab color to the soil. This is especially true in acid 
soils, in poorly drained ones, and in subsoils beneath peat, peaty 
loam or muck. In the latter case the iron has been deoxidized so 
completely that the soil usually presents a uniformly light drab 
color. The most striking effect of deoxidation is seen in the acid 
soils where drainage is intercepted by an impervious clay stratum. 
The iron is so completely deoxidized that the subsurface stratum 
is frequently white. 

Soil constituents themselves in some cases may impart color 
to the 'Soil, as where an abundance of quartz sand is found, giving 
the soil a grayish or whitish cast. Sometimes mica is sufficiently 
abundant to produce a glittering appearance in the soil. In some 
parts of the Piedmont Plateau the mica formerly existed in granitic 
rocks in large crystals from one-half to one and one-half inches in 
diameter. When the rock decomposed, the mica remained as large 
flakes, giving the soil a glittering appearance. The color of soils 
may undergo some change, usually due to the loss of organic matter 
through cropping, but mostly because of erosion, producing yel- 
lowish brown or yellow color. 

5. Odor of Soils. — As a general rule soils possess a distinct but 
feeble odor, due to a very small amount of an organic compound of 
the aromatic family and analogous to that of the camphorated 
bodies. A very minute quantity is present, there being only a few 
millionths ^ of a per cent. 
12 



178 



SOIL PHYSICS AND MANAGEMENT 



6. Number of Particles. — From the work preceding, especially 
the tables giving the dili'erent grades of soil material, it will be 
seen that many soil particles are extremely small, and the number 
of these in a certain volume or weight of soil is very great. If the 
largest particles of clay, 0.001 millimeter in diameter, were spherical 
and could be arranged in colunmar form in a cubical box one inch 
each way, it would" contain 15,655,000.000,000 particles. The de- 
termination of the niimber of particles in a definite weight of soil 
can be made by dividing the weight of soil by the weight of a 
single average-sized particle, as given in the following formula : 
„ _ Weight of s oil (grams) 
Weight of a single particle 

Weight of one particle =i6~D^ X Sp. gr. 

N = the number of particles, D = the mean diameter of the soil particle 
in centimeters and }6~Jy = the volume of a sphere. The specific gravity- 
taken is 2.65. 

This, of course, assumes that the soil particles are spheres and 
are all reduced to the average diameter. The following table gives 
the number of soil particles per gram of soil : 

Number of Particles and Internal Surface of Soil Separates 

Bureau of soils groups 



Soil separates 



Diameter, mm. 



Fine gravel. . .'. 
Coarse sand. . . 
Medium sand. . 

Fine sand 

Very fine sand. 

Silt 

Clay 



2.000 -1.000 
1.000 -0.500 
0.500 -0.250 
0.250 -0.100 
0.100 -0.050 
0.050 -0.005 
0.005 -0.0001 



Number of particles 
in one graru 



213 

1,709 

13,668 

134,480 

1,709,400 

34,722,000 

46,296,296,000 



Surface 

area per 

gram, 

sq. cm. 



15.1 

30.2 

60.4 

129.3 

302.1 

824.8 

9,090.2 



Internal 

surface 

one pound 

sq. ft. 



7.3 

14.7 

29.5 

63.1 

147.5 

402.7 

4,439.4 



Illinois experiment station groups 



Coarse sand. . 
Medium sand. 

Fine sand 

Coarse silt 

Medium silt. . 

Fine silt 

Clay 



1.000 -0.320 
0.320 -0.100 
0.100 -0.032 
0.032 -0.010 
0.010 -0.0032 
0.0032-0.0010 
0.0010-0.00001 



2,506 

77,821 

2,506,265 

77,821,000 

2,506,265,000 

77,821,000,000 



34.3 

107.8 

343.0 

1,078.2 

3,429.8 

10,781.6 



5,596,597,275,0001 44,834.8 



16.7 

52.6 

167.5 

526.6 

1,675.0 

5,266.4 

21,896.1 



8. Shape of Particles. — Particles of many shapes and sizes 
exist in all soils. The shape varies with the origin. Soils formed 
from volcanic ash or dust are most irregular in shape and those of 
wind origin are more nearly uniform. The former have many 



PHYSICAL PROPERTIES OF SOILS 



179 



elongated or lath-like particles, while those of wind origin are 
generally rounded. Figure 87 gives some of these difEerences, both 
as to shape and size. The closeness of packing varies with the shape 
of the soil grains. As a general rule, the more uniform the size 
and shape the closer the packing under normal conditions. 




Fig. 87. — (After Merrill.) A. Showing angular character of quartz particles in decom- 
posed gneiss. B. Quartz granules from beach sand. C. Showing outlines of shreds of vol- 
canic dust as! Been under the microscope. Rocks, Rock- Weathering and Soils, Merrill. 
(Courtesy Ma^millan Co.) 

9. Arrangement of Particles. — There is no definite arrange- 
ment of particles in soils. Coarse sands approach more nearly uni- 
formity than any others. Theoretically, there are two general forms 
of packing or arrangement, the columnar, figure 88A, and oblique, 
figure 88B'. If the soil particles were spheres and of uniform size, 
the columnar arrangement would give 47.64 per cent of air spaee^ 



180 SOIL PHYSICS AND MANAGEMENT 

while the oblique form would give 25.95 per cent. The air space 
with columnar arrangement may be calculated very easily by taking 
a one-inch cubical box and tilling it with marbles of different sizes, 
varying from one inch to one-sixteenth inch in diameter, and com- 

c 




Fig. 87. 

puting the per cent of air space left in the box. The same calcula- 
tion may be made for the oblique arrangement, although it is much 
more difficult because of the mathematics involved. 

If instead of having solid particles, as in figures 88A and B, 
A B c 




Fia. 88. — Diagram showing the arrangement of soil particles. A, columnar or vertical; 
B, oblique; C, compound granules. 

each of these should be a compound granule (Fig. 88C) made up 
of many spherical particles with the same arrangement as the larger 
particles, the air space or porosity would be, for columnar arrange- 
ment, (17.64 per cent -f 47.64 per cent of 52.36 per cent)= 72.58 
per cent, or, for oblique arrangement (25.95 per cent + 25.95 per 



PHYSICAL PROPERTIES OF SOILS 



181 



cent of 74.05 per cent) =45.17 per cent. The latter pore space, 
45.17 per cent, is approximately that possessed by the medium and 
fine sandy loams; while the former, 72.58 per cent, is too high for 
soils unless under exceptional conditions. The coarse sands which 
approach to theoretical conditions most nearly show 33 to 35 per 
cent of pore space. The granular condition developed in a soil in- 
creases its pore space. 

10. Internal Area or Surface. — The total surface of the soil 
particles in a given volume or weight is called the internal area or 
surface of the soil, and is usually expressed in square feet, or acres 
per cubic foot. This is very important because it controls to a 
large extent the amount of hygroscopic and capillary or film 
moisture. A system of grades of soil particles based on the internal 
surface would be of great value. Since the surfaces of spheres 
vary as the squares of their radii or diameters, the internal surface 
of a soil varies inversely as these functions. This may be shown 
by means of marbles as above and calculating the total surface 
with each diameter for columnar arrangement. 

Area of Spheres in a One-inch Cubical Box with Columnar Arrangement 



Diameter of spheres 



1 inch 

3^ inch 

J^ inch 

1/8 inch 

1/16 inch 

1/1000 inch 



Number of spheres in one 
cubic inch 



64 

512 

4,096 

1,000,000 



Total surface, square inches 

3.1416 

6.2832 

12.5664 

25.1128 

50.2256 

3,141.16 



The following table gives the internal area of various soils: 
Computed Surfaces of Soil Particle? in Different Kinds of Soil King ' 



Kind of soil 


Effective 
diameter of 
soil grains 


Pore space 


Surface of 
soil grains in 
one cubic foot 


Area per 
cubic foot 


Finest clay soil 

Fine clay soil 


mm. 

.004956 

.007657 

.008612 

.01111 

.02542 

.01810 

.02197 

.02619 

.03035 

.07555 

.1119 

.1432 


per cent 

52.94 
45.69 
48.00 
44.15 
49.19 
47.10 
44.15 
34.49 
38.83 
34.45 
32.49 
34.91 


square feet 

173,700 

129,100 

110,500 

91,960 

70,500 

53.490 

46,510 

45,760 

36,880 

15,870 

11,030 

8,318 


acres 

3.98 
2.96 


Fine clay soil 

Heavy red clay soil 

Loamy clay soil 

Clavev loam 


2.56 
2.11 
1.64 
1.23 


Loam 


1.06 


Loam 


1.05 


Sandy loam 


.84 


Sandy soil 


.36 


Sandy soil 


.25 


Coarse sandy soil 


.19 



182 SOIL PHYSICS AND MANAGEMENT 

From the preceding table it will be seen that the total surface 
area of the particles of a cubic foot of very line soil is about four 
acres, while a clayey loam contains an area of 1.2o acres per cubic foot 
and a coarse sandy soil about one-lifth of an acre. Careful calcula- 
tions show that a silt loam contains from Go,000 to 75,000 square feet 
per cubic foot. Taking a soil with an internal surface of 70,000 
square feet per cubic foot, the area of the particles in an acre to a 
depth of one foot would be about 109 square miles, or three town- 
ships. To a depth of four feet, from which plants t^ike most of 
their moisture, the total area of the soil particles in the silt loams 
is not far from 43(.> square miles per acre, or twelve townships. 
The capillary water is distributed over this surface. If the roots of 
a corn plant did not pass beyond the middle of the rows, and no 
more than four feet deep, each hill would have approximately 51.3 
acres of soil particle surface from which to draw its stipply of 
moisture and food. 

The following table shows the variations in the internal surface 
of some of the common soil types in the loessial areas of the middle 
west : 

Internal Area of Soil Tirpes, Calculated from Their Physical Composition * 



Soils 



Internal area j)er cubic foot 



Dime sand 

BroNvn sandy loam. . . 
Yellow gray silt lotun. 

Brown silt loam 

Black clay loam 

Drab clav 



square feet 


ijcrt-s 


30,310 


.696 


55,380 


1.271 


69,780 


1.602 


70.900 


1.62S 


S1.7S0 


1.S77 


13l\700 


3.13S 



11. Porosity of Soils. — Porosity is the total amount of air 
space in soils and is usually expressed in per cent of volume. It 
depends upon the relation of solid particles to the interstitial space. 
This is modified to a large extent by the size and shape of the par- 
ticles, granulation, tillage and amount of organic matter. Porosity 
or total pore space varies inversely as the size of the soil particles 
and increases with their irregularity of form. For this reason 
volcanic ash soils possess great porosity. Granulation and good 
tilth increase the porosity of soils, and puddling diminishes it. 
Tillage exerts a favorable influence on porosity, but sometimes in- 
creases it to an injurious extent. Porosity varies directly as the 
amount of organic matter. It is usually lessened bv the rearranofe- 



PHYSICAL PROPERTIES OJ'^ SOILS 



183 



iiiciit of tlio soil particlt's upon widtiii,!;', t'spcciiill) in soils low in 
organic mailer. 

The porosity nia}' be determined l)y di\ idiii.i!,' llie dilViTcnce be- 
tween the real and the apparent speeilic; gravity by the real, or by 
the following formula : 

_, ., Real Sp, gr. - App. Si), gr. 
Porosity = ^^^ygp_ g^- 

'^rhc porosity ol" dill'ercnt grades of sand lias been determined 
in this way and the results are given in tlie following table: 

Porosity of Different Grades of Sand * 



Loose 



Compact 



1. Passes a sieve 20 meshes to the inch; held by a 

40-mesh 

2. Passes 40-mcsh; held by GO-mesh 

3. Passes 60-mesh; held by SO-iiiesh 

4. Passes 80-mesh; held by lOO-niesh . . 

5. Passes 100-mesh. It contains all of the line 

particles 



per cent 

40.04 

42.07 
44.64 
45.92 

4(5.00 



per cent 

36.83 
37.69 
39.62 
41.39 

40.49 



The porosity of the soil under iield conditions is of much more 
importance than that of the laboratory sample, after having been 
finely ground. The laboratory determination gives comparative re- 
sults, however, that are of some value. The porosity may best be 
obtained by taking the apparent specific gravity under field con- 
ditions, as given on page 175, and the real specific gravity of the 
soil and use these in the formula above. Soils in good tilth have 
high i^orosity. It is not unusual for the same type of soil from 
different fields to have a difference of 10 per cent or even more 
of pore space in favor of the soil of good tilth. The total pore 
space varies inversely, while the size of the individual pores varies 
directly as the size of the particles. The total pore space of coarse 
soils as sands is small but the pores are large. ''J'he sectional areas 
of individual pores vary as the squares of the diameter of the soil 
particles. In figure 88 A there are IG pores per 'square inch, while 
if the particles are one-half as large they iiuml)er 64. The sectional 
area can be only one-fourth as large in the latter case as in the 
former. If coarse sand whose particles have a diameter of one- 
twenty-fifth of an inch is compared with clay who'se particles are 
one twenty-five-thousandth of an inch it will be seen that for sand 



184 



sou. riiYsics ANP mamc,i:ment 



with columnar arraui^vmoni ihovo will bo i>"-\'> povos por squavo iiu'h 
and with ohiv i>v\'\000,000. The I'onnor will bo ouo milliou timos; 
as largo as the hittor. The krge size ot* the pores permits certain 
physical pivcessos. sucli as pereohUiou ami aeration, to take ph\ce 
so readily that they may ho detrimental to tlie cn^p. On the other 
hand, tint^grainod soils, as clays and clay loams, with their very 
minute pores, hut large total pore space, may so retard pera^lation 
and aeration as to be e<]ually detrimental to the crop. Medium- 
graineii soils, as silt loiuni? or tine sandy loams jH>ssessing an inter- 
mediate pore space, are host suited to most crops, although both the 
coarse and very tine soils have their advantages under certain con- 
ditions. The size of the pores in tirie-graine<l soils is increased by 
gnuuilation. 

The following table shows the porosity of ditferent types of soils: 

Porosity in Soils of Varifd Physical Composition * 





natter eonteut 


Loose 


Compact 


SjuuI 


p<fr «■*»•* 
0.75 
2.90 
O.SO 
0.79 
4.SS 
5.50 
3.60 

W.4S 


ptr c«Ht 
44.9 
53.7 
59.0 
59.7 
lW.4 
61.2 
lv^.2 
65.6 


39.7 


Yellow t\uo knndy Uv\in *,loess) 

^^hito silt Uvuu 


43.3 
49.9 
50.2 


Brv'iNYn silt kvuu 


50.4 


Bl.'tck olnv loam 


52.7 


r)r;ib olsiv 


5S.2 


Peat '. 


tklS 







The total pore space of soils is rarely less than 30 per cent. 
Coarse, clean sand has about this amount. This means that a cubic 
foot of such soil will cn^ntain TO i^K'r ivnt of solid material. In case 
of shindy loams and silt loams, the pore spacx* amounts to about 50 
per (."ont. or half of the volimie of the soil. or. in a cubic t\xu. theiv 
are apprv>ximately SG'^ cubic inches of air space. The increase in 
pi^n^sity. within certain limits, is beneficial because of the increase 
in aeration. Extremely large air si^juh^s in soils are detrimental 
because they permit of exeessave evaporation. 

QUESTIONS 

1. Wh.^t is spool tio granty? 

i!. Givo sptx'itio irravity of a few ov^iimon soil-forming minerals. 

S. Wh.Ht is tho apparent speoitio gravity? 

4. How is it dotorM\iiuHl ? 

5. How doos jH^rosity atTtvt it? Tilth? 

I*. How is tho woisrht of a ovibio fix^t of soil dotormintxl? 



PHYSICAL PROPERTIES OF SOILS 185 

7. If a soil liaa an apparent Hpocifi(; gravity of 1.4, wliat in IIk; wciglit of 

the surface noil per acre? 

8. Why Ih eolor of soils so iniportaiit? 

!). What color is imparted by orj^aiii(! matter? 
10. W'liat ell'ect does limestoMc liave on color? 
] I. W'liat colors are due to ii'on? 

\A. Why are sulisoils in swamps so frequently gray or drab? 
l.'i. The subsoil above the tight clay stratum is usually gray in color. Why 
is this? 

14. What is peculiar of the subnoils of the Piedmont I'lateau? 

15. What soil constituents impart color? 

l(i. Explain how soils may undergo change in color. 

17. What can be said of the odor of soils? 

18. If soil particles average 0.02 inch in diameter, hftw many (iould be i)]aced 

in a one-inch cubicial box with columnar arrangemcint? If 0.0'i mm.? 

19. How many particles in a gram of soil if the particles average O.OO,") mm. 

in diameter? 

20. Upon what does the shape of the particles depend? 

21. What property does this all'ect? 

22. JJeline internal surface of a soil. 

23. How does the internal surface vary? 

24. How do the areas of spheres vary? 

25. If a cul)ic foot of soil has an internal surface of 50,000 square feet and 

it contains 20.8 pounds of moisture, how thick would the film of 
water be if unifoi'mly distribut(!d over the surface? 

20. What is the internal surface in a(;rcs of an acre of coarse sandy soil 
4 feet deep? (Table page 181.) 

27. Of an acre of the clay soil as given in the table on page 182? 

2'8. What two arrangcmi^nts for soil particles? 

29. If a two-inch cubical box is filled with shot one-sixteenth of an incli 

in diameter arrangcnl in columnar form, how many will it liold? 

.30. What per cent of air space will remain? 

31. How is the porosity modified? 

32. What effect does wetting have on total pore space? 

33. How is porosity of a soil determined? 

34. How is the porosity of a soil under field conditions determined? 

35. What relation betwen the total pore space and tli(> si/e of tin; pores? 

30. If soil particles are one-thousandth of an incli in diameter, spherical 

and arranged verti(;ally in a one-inch cube, what will be the total 
sectional area of the pores? Of a single pore? 
37. In the table on page 183 why is the porosity of the compact in 5 less 
than in 4? 

REFERENCES 

* Coffey, G. N., Bull. 85, Bureau of Soils, p. 42. 

^ Wiley, H. W., The Principles and Practice of Agricultural Analyses, 1000, 

p". 94. 
'King, F. H., Physics of Agriculture, Mrs. F. H. King, Madison, Wis., 1901, 

p. 124. 

* Unpublished data Soil Physics Division, University of Illinois. 



CHAPTER XIV 
WATER OF SOILS 

Plant growth cannot take place without moisture. Plants con- 
sist of from 60 to over 90 per cent of water. This represents only 
a very small part of the water used, since many plants transpire in 
twenty-four hours an amount equal to their weight. Water is of 
primary importance in many physical and all chemical changes 
that take place in the soil. 

Some Physical Characteristics of Water. — Water has certain 
physical characteristics that should be noted here. Its volume 
changes with temperature. Its maximum density is attained at 4 
degrees C, 39.2 P., and expansion takes place either above or below 
this temperature, and at 15 degrees C, 59 P., the density as com- 
pared with water at i degrees C. is 0.99. At the freezing point the 
density of water is 0.99988, while the density of ice at the same 
temperature is 0.928. In the melting of ice a large amount of heat 
is used, but it does not raise the temperature. This heat becomes 
latent or is used in changing the condition of the water from a 
solid to a liquid. It requires more heat to melt (fuse) ice than to 
fuse metals. To melt one gram of ice requires 80 calories,* whereas 
metals require from 5 to 77 calories. Expressed in Fahrenheit- 
pounds, the English system, the figures are 114 for ice and from 
9 to 138'.6 heat units for metals. 

In the evaporation of water a similar phenomenon is observed. 
When the boiling point is reached no further change in temperature 
of water occurs, but the heat is used in changing the water from 
a liquid to a gas. To effect this change in one gram 537 calories 
are necessary, or. with the Fahxenheit-pound, 966.6 heat units. It 
must be remembered that when water evaporates, an amount of 
heat equivalent to the above is used, regardless of the temperature. 
In changing from a higher to a lower temperature, or from gaseous 
to liquid form, or from liquid to solid, equivalent amounts of heat 
are liberated. , 

* A calorie, in general, is the amount of heat required to raise the tem- 
perature of a gram of water one degree centigrade. A heat unit or a British 
thermal iinit is the heat required to raise one pound of water one degree 
Fahrenheit. 

186 



WATER OF SOILS 187 

Specific Heat. — The amount of heat required to raise one unit 
mass of a substance one degree in temperature as compared to that 
of the same weight of water is the specific heat of a substance. The 
specific heat of water exceeds that of every other substance and is 
used as the standard or 1.0. Substances witli low specific heat 
change temperature rapidly. 

Viscosity. — The fluidity or viscosity of water varies with tem- 
perature and with substances in solution. If at degrees C, the 
viscosity is 100; at 50 degrees C. it is 31. 

Some substances when dissolved in water increase the viscosity, 
while others decrease it. 

Uses of Water. — Green plants contain a very large percentage 
of water, as stated above. A constant stream is passing in through 
the roots and transpired by the leaves. From 300 to 500 pounds 
of water are required for every jDound of dry matter of the plant. 
The soil then must contain a sufficient amount and must be of 
such character that it can deliver to the plant this enormous amount. 
If this is not supplied, the j)lant is stunted or may wilt and die 
before maturity. The uses of water in soils are as follows : 

(1) Directly as a plant food, taking part in the building up 
of tissues, either as water or indirectly by being used in combina- 
tion with other elements. 

(2) As a solvent for various substances in the soil that may be 
used by plants. It was believed by Jethro Tull that plants fed 
directly upon the very fine soil particles, taking them in through 
the roots, and that this accounted for the better growth of crops in 
well pulverized soils. 

(3) As a means by which these nutrient solutions are brought 
to and taken into the plant, either along with the water or by 
diffusion. 

(i) As a regulator of certain physical phenomena. 

(5) As an aid to chemical action produced directly or through 
the agency of bacteria. 

The Amount of Water Required by Plants. — Experiments 
have been carried on in various parts of the world by different 
investigators to determine the amount of water used in producing a 
crop. More or less transpiration is going on constantly during 
growth, and an enormous amount of water passes out through the 
stomates of the leaves. The following table gives the amount of 
water required to produce a pound of dry matter, as determined by 
different investigators. 



188 



SOIL PHYSICS AND MANAGEMENT 



Water Tninspiird by Growing Pla)it^ for One Part of Dry Matter Produced 



Lawes a«d Gilbert/ 
Eughuid 



Hellriegt'l,* Germanj- 



WoUn^-.t Germany Kiug,| Wisconsin 



Beans 214 

AVhoat -Jl'o 

Peas 2;^o 

Hevl clover . . . 24 i> 

Bjulev 202 



Beans (.horse"* 262 
NN" heat (.sprinsi^ooO 

Peas 

Red clover.... 

Barlev 

Oats," 

Buckwheat . . 

Lupine 

Kye ^spring). 



Maize 233 

Millet 416 



202 
330 
310 
402 
371 
373 
377 



Peas 

RiU^e 

Barley 

Oats 

Buckwheat . 
Mustarvi . . . 
Svmtlower . . 



447 
912 
774 

665 
W6 
S43 
4iH) 



Corn i.n\aize) 
Potatoes. . . . 

Peas 

Red clover . 

Barlev 

Oats 



271 
3So 
477 
577 
464 
5tU 



Averiige.... 237 Average... 342 



A\'erage... 603 Average.. 446 



* Hellriosel* vistxl quart i sand in siuiill amounts and supplied the neoessjtry plant food 
m solution. V'isutvs iuolude some K>ss oi water by evaporation, whioh was not prevented 
at first, but later rei.iui.-ed by means of covers. 

t WolloN-' usts.i small ^luaatities of sand well supplied with organio matter. Ferforatetl 
covers materially reviuoevl evaporation; this, however, was cheeked up on soil growiui; no crop. 

J Kiiur* use\l about 4t.K> vuniuds of normal soils, in cans, some set down in the earth. Some 
weri> ruu in tlie tield. others in grt>euhouses. Water was added from beneath, so that evap- 
oration was very sli^tht. 

Wo soo from the above table that the water re^iuired to pro- 
duoo one pound of dry matter varioi? from "^4 pounds iu the ease of 
Ivans, as dotonuiuod by Lawes and Cvilbert, of Euglaud. to iU".? 
pounds for rape, as determined by Wolluy, of Germany. The average 
of all determinations shown above is 4"JS pounds. King's deter- 
minations in Wisconsin probably apply bolter for the humid see- 
tion of this country than any others that have been made. The 
number of trials made by Kiitg was as follows: Teas, 1; barley, 
5; potatoes, 14; oats, "^0; clover, 46, and corn (maize), 5"^. With 
the water requirements as determined by King, a 100-lnishel crop 
of corn would require apptwximately 16 inches of water to produce 
it, or IS tons per busliel of grain; a 100-bushel crop of oats, about 
18 inches, or ".H^ tons ^nn- bushel ; a 50-bushel crop of wheat. 1"<?.T 
inches, or J^S.T tons per bushel, and a four-ton crop ot' clover, vO 
inches of water. 

Brigg-s and Shant^: have made determinations of water require- 
ments of plants in the arid regions of the United States, and their 
results are given in the tabic, page v4x. 

Dependent Upon Transpiration. — The amount of water 
required by plants is dependoi\t ttpon the atnotmt of transpiration, 
which in turn de^x^nds upon several factors, as follows: 

(1) High temperatures increase and low temperatures retard 
transpiration. 

(•<?) Movement of tiie air increases transpiration from the plant. 



WATER OF SOILS 



189 



while llic iiiovciiiciil of I lie plant ilsclf aids the circulation oL' ilie 
water wiiliiii tlic plant, and so increases transpiration. 

(3) Jjovv humidity is i'avorablu to transpiration. 

(4) The character of tiie soil is an important factor. More 
transpiration takes place from plants on poor soils than on those 
well supplied willi plant food. 

(,0) Transpiration increases with tlu; hrij^htness of the 
sunshine. 

(()) The moi'c moisture there is in the soil the f^^rciafer is the; 
transpiration. 

The Supply of Moisture in Soils, — 1. Rainfall. — TIk; supply 
of moisture in soils depends primarily on the rainfall. The excep- 
tions are where artificial irrigation is practic^ed or where water is 
br()ught to a region through some porous substratum and then 
reaches the surface by hydrostatic y)ressi]re. "^Phe following table 
shows the annual precipitatioji for dilferent portions of the earth's 
surface : 

Precipitation on Earth's Surface ^ 



■'■ Annual precipitation 


PcrcciitaK'! of aurtli'ti 
land Burfaco 


Under 10 inches : 


25.0 


From 10 to 20 inches 


30.0 


From 20 to 40 inches 


20.0 


From 40 to 00 inches 


11.0 


From ()() to (SO inclies 


9.0 


From SO to 120 inches 


4.0 


From 120 to 100 inches 


0.5 


Above 100 inches 


0.5 








100.0 



It is seen from the table that 55 per cent of the land area 
receives less than 20 inches of rainfall annually, while only 5 per 
cent receives over 80 inches. In the United States fully 50 per cent 
of the total area receives less than 20 inches of rainfall, and over a 
very large part of this the growing of crops is practically impossible 
except under irrigation. (See liainfall Map, 1^'ig. <Si).) In almost 
all regions where crops depend upon rainfall, its unecpial distribu- 
tion, or the frequent recurrence of pei'iods of drouth, results in 
reducedjields. 

In almost every season in some.})arts of even so small an area 
as a single State crops are injured to a greater or less extent by 
drouth. In some cases the dry weather occurs early in the sj^ring, 



190 



SOIL PHYSICS AND MANAGEMENT 




WATER OF SOILS 191 

in April or May, but it occurs more often in July or August, at the 
time when the growing crops are in greatest need of moisture. At 
the University of Illinois '^ the distribution of rainfall is so irregular 
that in the past twenty-five years seven Aprils have been dry or 
have had less than two inches of rainfall, and during this same 
time four Mays, eight Junes, five Julys, six Augusts, and eleven 
Septembers have been dry, or a total of 41 out of 150 growing 
months for the 25 3^ears. In the southern third of the State the 
distribution is still more irregular, and drouth is more injurious 
there, because of the greater evaporation and the character of the 
soil. This illustrates quite well the conditions generally in the 
humid area. 

2. Soil. — The supply of moisture for the crop depends upon 
the character of the soil itself. An open porous soil, such as a 
coarse sandy loam or sand, will lose a great deal of moisture by per- 
colation, and hence will not have a large supply for crops. Fre- 
quent rains are necessary for 'such a soil. However, the " firing " 
of the crop on sandy soil is not always an indication of lack of 
moisture. On finer grained soils, however, the moisture is retained 
much better and an abundant supply is usually present for the 
growing crop. The retentive power of the soil is increased very 
materially by the presence of organic matter. Probably no one 
constituent plays a greater part in maintaining the supply of moist- 
ure in the soil than that of organic matter. 

3. Loss by Evaporation. — In a soil deficient in organic mat- 
ter, consisting of medium-sized soil particles, the movement of 
moisture to the surface and its evaporation may reduce the supply 
sufficiently to injure the crop. This factor is of especial importance 
in semi-arid and arid sections. (See Chapter 18.) Mulches, good 
tilth, and a fair supply of organic matter reduce evaporation to a 
large extent. 

Ways of Expressing Moisture Content. — The moisture con- 
tent of soils has been expressed in a number of different ways, some 
of which have been discontinued because of their impracticability. 
Some of the methods are as follows: (a) per cent based on weight 
of soil; (b) in cubic inches or per cent of volume, and (c) in acre 
inches. 

(a) Per Cent of Weight of Soil. — In expressing the moisture 
content in per cent various methods have been used. A few inves- 
tigators have based it on the weight of the wet soil as taken from 
the field. This is not satisfactory, because the base varies from day 
to day as the moisture content changes. In some cases the per cent 



192 SOILS PHYSICS AND MAJS[AGEMENT 

has been based on the air-dry soil, and while this is somewhat better 
than the former, yet it is subject to the same objection, since the 
air-dry soil varies with the temperature and humidity of the air. 
Without doubt the most satisfactory base for expressing the per cent 
is the weight of water-free .soil obtained by drying in an oven at 
100 to 110 degrees C. Hilgard has used the temperature of 200, 
others 140 degrees C, for obtaining the water-free soil, but 
in general practice a temperature of 100 degrees C. is easier to 
maintain and just as satisfactory. Probably none of these is the 
exact point at which all of the hygroscopic moisture is driven off. 
The thing desired is a uniform standard. 

(b) Cubic Inches or Per Cent of Volume. — Expressing the 
water content in cubic inches or per cent of volume may have its 
advantage in case of certain soils, such as peats, or mucks, which 
are very light, or sands which are heavy. A peat soil with 50 per 
cent of moisture may contain no more than a silt loam with 20 per 
cent. A cubic foot of peat, water-free, weighs about 30 pounds, and 
50 per cent of moisture would mean 15 pounds per cubic foot, while 
the silt loam, weighing 75 pounds per cubic foot with 20 per cent, 
would have the same amount. Expressed in per cent of volume, the 
amount would be 24 in each case. To determine the per cent of 
volmne necessitates the finding of the per cent of moisture based 
on the water-free soil. 

(c) Acre-inches, — It is often desirable to express the water 
content of soils for convenient comparison with the rainfall. This 
may be done in square-foot-inches or in acre-inches, the depth of 
water in inches over a square foot or an acre. To do this it is neces- 
sary to determine the weight of water in the soil per square foot to 
the depth desired. The weight of water in a cubic foot in pounds 
divided by 5.2, the weight of a square-foot-inch of water, will give 
the depth in inches. 

QUESTIONS 

1. What amount of water is required hy plants? 

2. Give the effects of temperature clianges on water. 

3. What is latent heat? 

4. Give comparison of metals and water as to the amount of heat required 

to change the condition or state. 
.5. Give differences between the calorie and English heat unit. 
C). Define specific heat. 
7. How does water compare with other substance's? 

5. What factors modify viscosity? 
0. Give iises of wat«r in soils. 

10. How much water is required for a pound of dry matter? 



WATER OF SOILS 193 

11. How much for a 50-busliel corn crop? A 60-bushel oat crop? 

12. Upon what does the amount of water used by plants depend? 

13. How much of the earth's land surface is adapted to ordinary humid 

agriculture? 

14. What part of the United States is humid? (See Rainfall Map, Fig, 86.) 

15. How does the rainfall vary during difi'erent months? 

16. How does soil afl'ect the moisture supply? 

17. What part does evaporation play in the storage of water? 

18. What are the advantages and disadvantages of expressing moisture 

content in per cent of weight of soil? 

19. What is the best base to use? Why? 

20. Give advantages of expressing moisture content in cubic incheg or per 

cent of volume. 

21. Why is it well to express the moisture content in acre-inches? 

REFERENCES 

^Lawes and Gilbert, Jour. Hort. Soc, 1850. 

^ Hellriegel,. Experiment Station Record, IV, p. 532. 

^ Wollnv, Experiment Station Record, IV, p. 532. 

*King,'F. H.. Physics of Agriculture, 1907, p. 139, also 11th and 14th An- 
nual Reports Wisconsin Station. 

"Widtsoe, J. A., Dry Farming, 1911, p. 33. 

' Mosier, J. G., Bulletin 204, Illinois Experiment Station, Climate of 
Illinois, 1917. 



13 



CHAPTEE XV. 



WATER OF SOILS 



I. HYGROSCOPIC MOISTURE 

Water is held iu soils by the manifestation of attractive force 
under three forms: (1) hygroscopic, or adhesion; (2) surface 
tension, and (3) hydrostatic, or gravity. These give rise to the 
three so-called forms of water — hygroscopic, capillary, or film, and 
gravitational. It must be remembered that the water of all is the 
same in chemical composition, the only difference being in the force 
holding or moving it in the soil. 

Hygroscopic Moisture. — All substances have the power of con- 
densing moisture upon their surfaces, hence a very thin film of 
water exists around all substances exposed to the air. This phenom- 
enon is known as adsorption. The water is held very firmly by ad- 
hesion or molecular force, which is estimated as equal to 10,000 
atmospheres, and the water may be removed only by a temperature 
much higher than the ordinary. When normal temperature is 
restored, the moisture will again be slowly condensed upon the sur- 
face. Briggs ^ has calculated the thickness of the hygroscopic film 
for quartz particles as 2.66 X 10-® centimeters, or 0.0000266 milli- 
meter. The amount of hygroscopic moisture in a soil defends upon 
several factors. 





Hygroscopic 


Capacity of Soils - 




Soil 


Amount 
of clay 


Minimum 
moisture 


Maximum 
moisture 


Average 


Sandy soils 

Sandy loams 


per cent 

Less than 5 

5 to 10 

10 to 15 

15 to 20 

Over 20 


per cent 

0.79 
1.84 
2.30 
5.06 
4.20 


per cent 

4.18 

6.12 

9.18 

10.26 

18.60 


per cent 

2.59 
3.39 


Loams 


5.19 


Clay loams 


6.49 


Clays 


10.83 









(a) Size of Particles. — The amount of hygroscopic moisture 
in soils varies inversely as the size of the particles and directly as 
the internal surface of the soil. Since colloids are made up of very 
minute particles, a small amount present v\all increase very mate- 
rially the internal surface and consequently the total amount of 
194 



HYGROSCOPIC MOISTURE 



195 



this form of moisture. Sandy soils with a relatively small surface 
area contain only small amounts of hygroscopic water. 

The preceding table shows the amount of hygroscopic moisture 
as determined by Hilgard. The soils were exposed in saturated 
atmosphere at 15 degrees C. and dried at 200 degrees C. 

This shows the effect of texture and consequently the internal 
surface upon the amount of hygroscopic moisture. In another case 
the hygroscopic capacity was determined for the whole soil and then 
for the separates as follows : 

Per cent 

Whole soil 5.24 

Clay 17.60 

Hydraulic Value less than 0.25 mm. per second. . . . 7.96 

Hydraulic Value 0.25 mm 2.91 

Hydraulic Value 0.50 mm 1.73 

(b) Colloids. — The colloids have a very high adsorptive power 
for water, and their presence in soils increases very strikingly the 
hygroscopicity. Nearly all soils, and more particularly the heavy 
ones, contain considerable amounts of colloids. They may occur 
as humus, ferric oxide, silicic acid, or hydrous aluminum silicates. 
Hydrated ferric oxide and some other minerals may unite with 
water chemically, but the common hygroscopic phenomenon is one 
of adsorption. This table shows the eifect of colloids on the hygro- 
scopic moisture. 

Influence of Silt, Sand, Clay, Ferric Hydrate and Humus on Hygroscopic 

Capacity ' 



Missis- 
sippi 
pine 
hills 

sandy 
loam 



Wash- 
ington 
dust 
soil 



Missis- 
sippi 
white 
pipe 
clay 



Missis- 
sippi 
flat- 
woods 
clay 
soil 



Missis- 
sippi 
ferru- 
ginous 

clay 

soil 



Oahu 
ferru- 
ginous 
laterite 



Missis- 
sippi 
marsh 
muck 



Missis- 
sippi 

marsh 
soil 



Hygroscopic moisture 

Clay 

Ferric hydrate .... 

Humus 

Finest silts (0.01- 

0.0250 mm.) 

Sands, fine and me 
dium (0.0250-0.50 
mm.) 



2.48 

2.94 

1.64 

.55 

60.10 



31.20 



4.92 
1.27 

"!44 

45.04 

42.40 



9.09 

74.65 

.15 

0.00 

23.15 



.20 



9.33 

25.48 

"!50 
68.60 

4.70 



18.60 
28.15 
12.10 
little 

40.33 



15.61 



19.66 
? 

5i!oo 

3.33 



45.66 



21.00 
Tr. 

66!io 

33.94 



15.40 
Tr. 

19.83 

8.70 



70.18 



It will be seen from the above table that clay, ferric hydrate and 
humus have the greatest effect upon hygroscopic capacity. 

(c) Temperature. — The temperature affects the amount of 
hygroscopic moisture, since under temperatures higher than normal 



196 



SOIL PHYSICS AND MANAGEMENT 



a jjart of the hygroscopic moisture is driven off. Condensation will 
again take jDlace when the temperature becomes lower. If, however, 
the air is saturated with moisture an increase in temperature 
increases the amount of moisture adsorbed. 

Hilgard has found that a fine sandy soil that adsorbed two per 
cent of moisture from- a saturated atmosphere at 15 degrees C. 
adsorbed four per cent when the temperature was raised to 34- 
degrees C. A heavier soil which adsorbed seven per cent in a satu- 
rated atmosphere at 15 degrees C. adsorbed nine per cent at 34 
degrees C. 

(d) Organic Matter has a high adsorptive power for water, 
especially in the form of colloidal humus. All soils contain this in 
small amounts, at least, while some have several per cent, which 
gives them a high hygroscopic capacity. 

(e) Humidity. — The changes in humidity of the air cause a 
variation of hygroscopic moisture at the same temperature. If a 
soil adsorbs one unit of moisture in a saturated atmosphere at a 
certain temperature, it will adsorb three-fourths* of a unit when 
the air is three-fourths saturated, and one-half unit at one-half 
saturation, but at one-fourth saturation will adsorb slightly more 
than this proportion. 

Dobeneck has sho-wm the effect of various relative humidities 
on the hygroscopic content of quartz and humus after an exposure 
of 24 hours at 20 degrees C. 

Percentage of Hygroscopic Moisture {Dobeneck) ^ 



Relative humidity 
per cent. 


30 


50 


70 


90 


100 


Quartz 

Humus 


0.045 
4.055 


0.053 

7.765 


0.76 
10.589 


0.119 
15.676 


0.175 

18.014 



The Determination of the Hygroscopic Coefficient of Soils. 

— The hygroscopic coefficient of a soil is the amount of moisture it 
will adsorb when exposed to a saturated atmosphere for a definite 
time at a constant temperature. 

The determination of the hygroscopic capacity or hygroscopic 
coefficient of soils is of considerable importance, since it gives a 
constant for the soil that depends upon the internal surface, thus 
giving a means of comparison. One of the best methods for its 
determination is that of Briggs, which is to place the soil in a satu- 
rated atmosphere at 75 degrees F., approximately 24 degrees C, and 
let it remain until no further increase in weight is shown. It is 



HYGROSCOPIC MOISTURE 



197 



then dried at 100 degrees C. The difference gives the h^'groseopic 
coefficient of the soil. Hilgard lias used a temperature of 200 
degrees C. in the determination of hygroscopic capacity, which 
comes nearer, probably, reaching the point of absolute dryness of 
soil. In this determination the soil should be spread out in a very 
thin layer, so that as large a, surface as possible may be exposed 
directly to the saturated air. 

The hygroscopic coefficient of soils may be, determined indirectly 
by using other constants to which the hygroscopic coefficient bears 
a definite relation. The formulae are as follows : 

(a) Hygroscopic coefficient ^ ^ wilting coefficient X 0.68. 

(b) Hygroscopic coefficient ^moisture equivalent X 0.37 

(c) Hygroscopic coefficient = (moisture holding ca 



X 0.234. 

(d) Hygroscopic coefficient = 0.007 
-j- organic matter ) . 



holding capacity — 21) 
sands + 0.082 silt + 0.39 (clay 



For wilting coefficient see page 212; moisture equivalent, page 
202, and moisture holding capacity, page 209. 

The Use o£ Hygroscopic Moisture. — It was formerly believed 
that plants were able to use some hygroscopic moisture, but later 
investigations seem to show that this is not possible. Permanent 
wilting has been taken as the point at which plants cease to obtain 
sufficient water from the soil, and at this point they still contain 
some capillary moisture, although the film is quite thin. 

Determinations of the moisture content of soils at wilting have 
been made by Briggs and Shantz, and are given in the following 
table : 

Relation of Hygroscopic Coefficient ^ to the Wilting Coefficient 



Hygroscopic 
coefficient 



Wilting 
coefficient 



Amount of 

capillary water 

remaining 



Coarse sand 

Fine sand 

Sandy loam 

Fine sandy loam 

Loam 

Clay loam 



per cent 

0.5 
1.5 
3.5 
6.5 

7.8 
11.4 



per cent 

0.9 
2.6 
4.8 
9.7 
10.3 
16.3 



per cent 

0.4 
1.1 
1.3 
3.2 
2.5 
4.9 



In the work of Briggs and Shantz the determination of the 
wilting coefficient of soils always shows the presence of some capil- 
lary water. Even at the death point of plants soils show more than 
the hygroscopic water present. 



198 SOIL PHYSICS AND MANAGEMENT 

Hilgard ^ gives the following uses of hygroscopic moisture in 
plant growth : " ( 1 ) Soils of high hygroscopic power can with- 
draw from moist air enough moisture to be of material help in 
sustaining the life of vegetation in rainless summers or in time 
of drouth. It cannot^ however, maintain normal growth save in 
the case of some desert plants. (2) High moisture absorption pre- 
vents the rapid and undue heating of the surface soil to the danger 
point, and thus often saves crops that are lost in soils of low hygro- 
scopic power." 

QUESTIONS 

1. What forces act upon water in soils? 

2. What forms of moisture are found in soils as a result of these forces? 

3. Define hygroscopic moisture. 

4. How does size of particles. affect the amount of hygroscopic moisture? 

5. What effect do colloids have? 

6. Wliat effect does temperature have on hygroscopic moistvire in com- 

paratively dry air ? 

7. What effect if the air is saturated? 

8. What effect does organic matter have on hygroscopic moisture ? 

9. What relation exists between the adsorption of soils from different de- 

grees of saturation? 

10. How do the ratios of humidity and adsorption compare in the table on 

page 196? 

11. Define hygroscopic coefficient. 

12. How is it determined? 

13. Can plants use hygroscopic moisture? 

14. Which soil in the table on page 197 has the highest hygroscopic co- 

efficient? Why? 

15. Which contains the highest amount of capillary moisture after the wilt- 

ing coefficient is reached ? 

16. If a clay loam soil weighs 80 pounds per cubic foot, how many tons 

of unavailable moisture is in the soil to a depth of two feet per 
acre? (See table on page 197.) 

17. What is the use of hygroscopic moisture? 

18. The wilting coefficient of a clay loam is 16.2 per cent, what is the 

hygroscopic coefficient ? 

19. If the moisture holding capacity of a soil is 23.2 per cent, what is the 

hygroscopic coefficient? 

20. If a soil contains 83.1 per cent of sand, 8.6 of silt and 7.5 of clay, what 

is the hygroscopic coefficient? 

REFERENCES 

^Briggs, L. J., Journal of Physical Chemistry, Vol. 9, 1905, pp. 617-641. 

^^ Hilgard, E. W., Report of the California Station, 1892-3-4, p. 70. 

^Hilgard, Soils, 1906, p. 196. 

*0p. Cit., p. 198. 

"Dobeneck, A. F., Von Untersuchungen iiber das Absorptionsvermogen und 

die HygroskopizitJit der Bodeukonstituenten. Forsch. a. d. Gebiete 

d. Agri.-Physik., Band XV, 1892, Seite 163-228. 
•'Briggs, L. J., and Shantz, H. L., Bulletin 230, Bureau of Plant Industry, 

U. S. D. A., The Wilting Coefficient for Different Plants and its Indi 

rect Determination, 1912, p. 73. 
' Op. Cit., p. 65. 
» Hilgard, Soils, 1906, p. 200. 



CHAPTER XVI 



WATER OF SOILS 

II. CAPILLARY WATER 

The most abundant and by far the most important form of soil 
moisture is capillary or film moisture. It differs from hygroscopic 
moisture in that it evaporates at ordinary temperatures, is not con- 
densed again on the soil particles, and may move from one particle 
to another. 

The term capillary as applied to this form of water has arisen 
from the fact that this movement may be best seen in very small 
capillary tubes. When tubes are placed in water the height to which 
it will rise varies with the diarneter of the tube. 

Height of Capillary Rise in Glass Tubes 





Diameter of tubes 


Height of water 


1.0 mm. 
.1 mm. 
.01 mm. 


15.336 mm. 

153.36 mm. 

1533.6 mm. 



The law expressing this action is as follows : The height to 
which the water rises varies inversely as the diameter of the tube. 
The reduction of the diameter one-tenth causes the water to rise 
ten times as high. The movement of water in soils from a free 
water surface resembles somewhat the movement of water in a large 
number of capillary tubes of various sizes. In the case of soils 
where the water rises from a free water surface the amount in the 
soil varies inversely as the distance above the free water. This 
would be exactly true of a large number of various-sized capillary 
tubes. The explanation for soils is not quite as simple, however, 
as this would indicate. 

Surface Tension. — Whenever an air- water surface exists the 
molecules of water in the interior are attracted equally in all direc- 
tions. The molecules on the surface are subjected to a double but 
unequal attraction of the water on one side and the air on the other, 
which has the effect of producing a thin film composed of the sur- 
face molecules which is under tension. If the film is flat no pres- 

199 



200 



SOIL PHYSICS AND MANAGEMENT 



sure is exerted in any direction. If curved the tension will cause 
a pressure in the direction of the center of curvature and in pro- 
portion to the radius of curvature. The pressure is equal to two 
times the tension divided by the radius. The greater the curvature 
the less will be the radius and consequently the greater the pressure. 
If soil particles are in contact the water will be in two forms : 
(1) as a film aromid the particles, and (2) as a waist between the 
particles as shown in figure 90. The pressure is always in the direc- 
tion of the center of curvature and varies inversely' as the radius. 
The pressure of the film around the soil particle is inward, while 
that of the waist is outward. The force will then be the difference 
between these two. As a general rule the waist film exerts the 
greater force because it has the greater curvature or the lesser 
radius. The pressure due to difference of curvature is well shown 
by two soap bubbles ^ a and d that have a free air passage between 
them as in figure 91. The curvature of the smaller, d, should give 





■"ra. 90. — Soil particles showing films 
and waists of capillary water. 



Fig. 91. — Large and small bubble con- 
nected by a tube b. The greater curvature 
of d forces the air into a until the curva- 
ture of c is the same as a. 



it greater pressure. That this is true is shown by ihe fact that the 
air is forced from it into the larger bubble, a, till the film, c, across 
the end of the tu)3e, has a curvature the same as that of the large 
bubble. 

If soil particles are in contact so that the water films coalesce, 
the films wiU adjust themselves so as to be in equilibrium. If, how- 
ever, water is removed from one of the particles, as at d, the equilib- 
rium will be destroyed, a pull will be set up toward d, and water 
will move from other particles until equilibrium is restored. In 
figure 90 the film around d is thinner than at a, and this may make 
a slight difference in the curvature of the films, but more particu- 
larly of the waists, the curvature being much greater between c and 
d than between a and h. The greater outward force at e and / 
would draw water from the other films. 

If water is added at u the equilibrium will be destroyed and 
readjustment will take place. The smaller the amount of water 
present in the soil the greater will be the curvature of the films 



CAPILLARY WATER 



201 



Moisture in Soil Columns. — A number of particles are ar- 
ranged vertically as in figure 92. The film around (1) is held 
by the attraction of that particle alone. The film around (2) is 
held by the' attraction of the particle, plus the outward pull of the 
waist at a. The water film of (3) is held by its own force, plus 
those of a and h. jSTo. (4) is held by its force, plus a, b, and c. The 
film of the loAver soil particle must be held by the greatest force, and 
as a result this particle would have the thickest film. If the lower 
end of the soil column contains free water the films may be so thick- 
ened by the combined force of the film above that nearly all pore 
spaces may' be filled with water. The pore spaces of the soil column 
in contact with the free water may act as tubes. 

Effect of Size of Soil Particles. — It will be seen from this, 
then, that the movement of capillary water is due to the difference 
in curvature of the film, and the greater the curv- 
ature the greater will be the capillary pull or 
pressure. The smaller the amount of water pres- 
ent in the soil, the greater will be the curvature 
of the film between the soil particles. As a gen- 
eral rule, the larger the number of soil particles 
the greater the number of films present, and 
consequently the greater pull will be exerted per 
unit of volume of the soil. Hence the water 
in capillary tubes represented by a single film 
at the top of '.the water • column will not rise as 
high as in the soil, where the number of films 
is many times greater than in the tube. 
Fig. 92.— Showing '^^^ height to which the water will rise de- 
theoreticaiiy the thick- pends upou the difference between the combined 

ness ot nlms in a ver- ^ >- 

ticai soU column. f orce of the films and the force of gravity rep- 

resented by the weight of the water. In coarse-grained soils, 
where the total film surface is small, this force representing the 
upward pull will soon be overcome by fEe^tovee of gravity or 
weight of water, and hence water will not rise very high. In finer- 
grained soils where the total surface of the films is very large it 
will require the weight of a very high column of water to balance 
this force, hence in fine-grained soils water will rise much higher 
than in coarse soils. 

In two soils, one fine-grained and the other coarse, having the 
films of the same thickness and the same curvature, there will be no 
tendency for water to move from one to the other when brought in 



202 



SOIL PHYSICS AND .MANAGEMENT 



coutect, although the tiiier-graint\i soil may have luanv time? the 
moisture oonteiit of the other. Ou the other hand, a ohiy soil may 
extract water from a saud soil when iu close contact, even if the 
clay contains several times the amount of water that the sand soil 
does. The ditference will be due to the fact that in the ca:se of the 
smaller soil particles in the tiner-graine^l soil the water lilm Avill 
have a greater curvature, and hence will be able to pull water from 
the sand soil, where the tilms have less curvature. 

Moisture Equivalent.- — Briggs and McLane designed a centrif- 
ugal machine by which moist soils could be subjected to a force of 
1000 times that of gravity or more. The soils under this condition 
would lose moisture until the capillary force was in equilibrium 
■\nth this force of 1000 times gravity, when no further loss would 
take place. At this point all soils have tilms of the same thickness, 
aiul if the soils are put in close contact there is no tendency for 
water to move from one soil to the other. The capillary forces are 
in equilibrium. The per cent of water present at this point is 
knoA^n as the moisiure equiralenf of the soil. It is always liigher 
than the wilting coefficient and lower than the optimum water con- 
tent. While not representing any critical moisture content, yet it 
furnishes a very convenient constant for comparison of different 
soils. The lutmerical value of the moisture equivalent depends upon 
the internal surface of the soil. The following table gives the 
average for some classes of soils : 

Moisture Equiixilents of Some Soil Classes * 



Maximum 


Minimum 


Averag 


7.3 


3.0 


4.9 


10.0 


3.S 


5.6 


1S.6 


5.3 


10.4 


21.4 


6.S 


13.0 


20.S 


7.7 


16.5 


26.9 


S.o 


17.1 


32.4 


15.1 


21.9 


3S.4 


10.1 


32.0 



Sands 

Fine s;inds 

Sandy loams. . . . . 
Fine s^mdy loams 

lA>ams 

Silt loams 

Clav loan^s 

ClaVs 



Since the nioisrure eqttivalent bears a rather delinite ratio to 
other soil constants these may be tised in its indirect determination. 

Determination of Moisture Equivalents from Other Soil 
Constants. — When tlie other soil constants, as wilting coetticient, 
hygroscopic coefficient, moisture holding capacity, or met.~-hanieal 
analysis, are known, the moisture equivalents may be determined 
indirectly bv the f oUowinsr formulae : 



CAPILLARY WATER 203 

(c) Moisture oquivalent =:( Moisture liolding capacity — 21) X -035 
(b) Moisture e<|uivalent= liyj'roscopic coi'llicient X 2.71 

(a) Moisture ecjuivulcut ^ Wiitin*^ coi-dicient X 1.84 

(d) Moisture (■(juivaleiit = 0.02 sand + 0.22 silt + 1.05 clay. 

Movement. — 'I'lie movement of capillary water may take place 
ill any direction, but with slightly greater facility downward than 
upward or sidewise, because of the aid of gravity. The rate and 
height of movement depend upon several factors. 

1. The Thickness of the Film. — One of the most important 
factors in capillary movement is the thickness of the film of water 
on the soil particle. As a general rule, the greater the difference 
between the moisture content of adjacent soil masses, or the greater 
the difference in the thickness of films, the stronger will be the pull 
and the more rapid will be the movement. This is very well shown 
in soils adjacent to free or gravitational water. The distribution 
near the free water takes place rapidly through capillary passages, 
while at some distance the movement is by means of thin films and 
slow surface distribution. If this movement is upward, it is re- 
tarded by gravity, but if downward, as after a rain, the movement 
becomes somewhat rapid, especially if the films are quite thick. 

To determine how rapidly or slowly water moves from a moist 
soil into a dry one, bury a dry clod two or three inches in diameter, 
in soil with medium moisture content, and examine every three or 
four days. The movement is very slow. Two or three weeks will 
be required for the clod to become moistened. It is without doubt 
true that the roots of plants go after the moisture rather than wait 
for the moisture to move to them by capillarity. This fact controls 
to a large extent the root development of plants. It must be remem- 
bered that very little capillary water used by plants is drawn from 
the water table of the soil, which is usually many feet beneath the 
surface. Plants sometimes wilt when the free water is not more 
than three or four feet beneath the surface, which means that the 
moisture rising by capillarity is not sufficient for the use of the 
plant. The fact that moisture moves so slowly through a dry soil 
is what makes dust mulches. so effective. 

In order to show the rate of movement of water through the 
soil, after the dry summer of 1889, King, of Wisconsin, collected 
samples of soil to a depth of five feet, and a portion of the dry area 
was effectually protected from Tain and snow and left in this con- 
dition until April the following year. Samples were then collected 



204 



SOIL PHYSICS AND ]^IANAGEMENT 



from the eo\ered and from the exposed soil and the moisture eon- 
tent determined. The results are iiiven in the table. 



ira/(7- Per cent of Dry Soil, Covered and Uncovered, at Diferent Dates i,A'm</)j 





Original soil 


Soil covered 


Soil uncovered 




Oct. 2S, 1SS9 


April 14, 1S90 


April 14, 1S90 


1st foot, sandy clav 


per cent 

4.03 
10.07 
9.11 
4.35 
4.53 


per cent 

3.32 
6.6S 
6.32 
3.71 
5.0S 


per cent 

20.23 


2nd foot, red clav 


20.01 


3rd foot, clay and sand 

4th foot, sand and gravel 

5th foot, sand and gravel 


S.32 
8.63 
6.07 


Mean 


6.42 


5.02 


12.65 







In the protected soil there was not only no gain hv capillarity 
from the sides or from below, but an actual loss occurred. 

•2. Viscosity. — Viscosity is the resistance that liquids offer to 
the inovemeut of molecules against each other. This property is 
well seen in syrups, hut we do not ordinarily think of water as pos- 
sessing any large amount of viscosity or showing any variation 
in this respect under ditferent conditions. A somewhat higher 
viscosity increases the surface tension of the film, but at the same 
time retards the rate of movement by lessening the fluidity and 
freedom of movement. 

(a) Tempera hi re. — Variations in tlie temperature of water 
change its viscosity, a higher temperature diminishing and a lower 
increasing it. Increasing viscosity increases surface tension. It 
has been determined that if the viscosity of water at zero C. is taken 
as 100, then the viscosity at 25 degrees is 50. at 30 degrees 45, and 
at 50 degrees ol."* This variation influences the capillary move- 
ment of moisture in soils to some extent. 

The next table shows that capillaxy movement is more rapid at 
higher temperatures, indicating that the greater fluidit}' produced 

Effect of Temperature on Rise of Capillary Moistvre,^ University of Illinois. — 
Height in Inches in 24 Hours 



Temperature, degrees 
Fahrenheit 


Brown silt 
■ loam 


White sat 
loam 


Yellow fine sandy 
loam 


32.5 
60.5 
70.5 


11.9 
13.3 
13.5 


11.9 
14.0 
14.5 


19.7 
22.9 
25.8 



CAPILLARY WATER 205 

is of greater importance tlianau increased tension,' at least within 
the limits of the experiment. While an increase in viscosity gives 
greater surface tension, the rate of movement is decreased because 
of greater resistance. Under higher temperatures the capillar}^ 
limit would be reached sooner, yet the height attained would be 
less than at lower temperatures. 

Somewhat dry soils frequently become moist in late autumn 
without rain. This is probably due to two ' things — less evap- 
oration due to lowering of temperature and increased capillary pull 
at the surface due to greater surface tension of the water at this 
temperature. 

(b) Substances in Solution. — The viscosity and likewise the 
surface tension of water are affected more or less by substances in 
solution. Some increase, while others decrease tension. The 
height to which liquids rise in soils varies with the surface tension, 
the densities of the liquids being the same. The rapidity of rise 
of those liquids in the same soil depends upon the viscosity : the 
more viscid the liquid the slower the movement. Mineral sub- 
stances added to a soil generally increase the surface tension. If 
potassium chloride is added to the surface of a soil the capillary 
pull of the surface moisture will be increased, and more water will 
be brought up from the subsoil. This is true of most mineral 
fertilizers. 

Organic substances lower the surface tension so that they would 
not cause so great capillary pull, but would increase the rapidity of 
movement. Soil solutions have a low surface tension. 

Eains wetting a few inches in depth have a tendency to draw 
water up from the deeper soil, as observed by King.^ He found 
that 3.5 pounds per square foot in one trial and 3.69 in another 
had been transferred from the lower soil 24 to 48 inches to the upper 
in 26 hours after wetting. This is due in part to the fact that the 
surface tension of rain water is greater than that of soil solutions. 

From the next table it will be seen that common salt gives the 
greatest tension and that soil solutions are low. If any of the 
chemical substances mentioned in the table should be applied to 
the surface of the soil when it passed into solution, the tension 
would be increased sufficiently to draw up water from below. Some 
recent experiments by Karraker ^ indicate that substances in solu- 
tion play little part in moisture movement. The strengths of the 
solutions in the table are ' much greater than probably ever occur 
in soils, unless it should be in the immediate surface just after an 



206 



SOIL PHYSICS AND MANAGEMENT 



Surface Tetmon ajui the Dejisity of Certain Solutions '' 



Solution 





Surface 


Density 


tension, dynes 




per sq. em. 


1.0000 


73.9 


1.1000 


77.6 


1.1000 


77.5 


1.1000 


76.8 


1.1000 


75.8 


1.1000 


75.8 


1.1000 


75.1 


1.0830 


75.1 


1.0038 


75.2 


1.0012 


77.4 


1.0013 


77.0 


1.0020 


75.5 


0.9600 


67.5 


1.0260 


64.9 


1.0013 


73.2 


1.0000 


71.0 


1.0000 


69.6 


1.0000 


69.4 



Water 

Common salt (NaCl) 

Muriate potash (KCl) 

Ammonium sulfate i(,NH4)2S04) 

Sodium sulfate (.Na-^SOJ 

Sodium nitrate (NaNOs) 

Potassium hydrate (KOH) 

Potassium sulfate (KsSO*) 

Wood ashes 

Thomas slag 

Marl 

Lime 

Aiimiouia (NH4OH) 

Urine 

Stable manure 

Kentucky blue-grass soil 

Wheat soil 

Garden soil 



applicatiou of some miueral fertilizer or in alkali soils. In either 
of these cases some effect would uudoiibtedlv be produced. 

3. Texture. — The smaller the soil particles the slower the 
capillary movement, but theoretically the higher the water will 
rise. This is true only in theory. The resistance to movement 
becomes so great in very line-grained soils that the water will not 
rise as high as in medium-grained ones. Loughridge found that 
in an adobe soil with 44.3 per cent of clay, a height of 4G inches 
was reached in 195 days, while in a line sandy soil the water attained 
a height of 47 inches in 125 days. In a sand soil the water reached 
its limit in six days. The movement of water in clay soils is very 
slow, not only due to the extreme "fineness of the ordinary clay 
particles, but to the presence of colloids which doubtless hinder 
the movement. 

In experiments with two soils water rose by capillarity 8.5 feet 
in 90 days in loess (yellow fine sandy loam), while in white silt 
loam soil with 0.8 per cent of organic matter it rose 9.5 feet in about 
the same time. The loess contained practically no organic matter. 

4. Organic Matter. — The presence of organic matter retards 
capillary movement, vine to the colloids present and the greater 
porosity produced. The next table shows the movement of water 
in soils by capillarity from a free water surface. The tubes were 
one and one-half inches in diameter and five feet long. 



CAPILLARY WATER 



207 





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208 



SOIL PHYSICS AND MANAGEMENT 



By comparing columns 1 and 2, 3 and -i, 5 and 6, 7 and 8, 9 and 
10, and then all with 11 in the table, the effect of organic matter 
may be seen. 

In the coarse-grained soils the organic matter which consisted 
of finely ground well-decomposed peat gives a greater range o'f 




Fig. 93. — Showing the effect of various amounts of organic matter on the rise of capillary 
water from a free-water surface for a 14-day period. 



CAPILLARY WATER 



209 



movement. It reduces the rajoidity at first, but the water in tlie 
mixture, as shown in column N"o. 2, passes jSTo." 1 in six hours. In 
the finer-grained soil the effect of organic matter is to not only 
retard the movement from the first, but to diminish the height, as 
shown, by comparing Nos. 3 and dt, 5 and 6, and 7 and 8. A com- 
parison of jSTos. 9 and 10 shows the effect of the removal of organic 
matter by cropping. Slow capillary movement is desirable in sur- 
face soils to prevent excessive loss of moisture by evaporation. The 
subsurface and subsoil are better adapted for more rapid capillary 
movement which brings the moisture up where roots in the surface 
soil may obtain their supply. The peat is an excellent example of 
very slow movement through a very porous soil. The limit was 
reached in ten days. Figure 93 shows the effect of organic matter 
on height of rise of water. 

Maximum Capillary Capacity or Moisture-holding Ca- 
pacity of Soils. — Soils possess varying powers of retaining moist- 
ure by capillarit}' due primarily to texture. The method of deter- 
mining this has been devised by Hilgard and modified by Briggs. 
A small cup five centimeters in diameter and one ^ in height, 
with the bottom made of very fine bolting cloth, is used. The soil 
is settled slightly by jarring and stroked off level with the top of 
the cup. It is then placed with the bottom in the water, and when 
the soil has taken up the maximum amount of water, it is allowed 
to drain for a few minutes, and the weight of the water determined 
by comparing with the weights of the drv soil. This weight is des- 
ignated as the water-holding capacity of the soil. This is much 
higher than will be found under field conditions. The following 
table shows the percentage of water held by capillarity and the total 
water at saturation in some soils, all from Illinois except the last. 



Maximum Capillary and Maximum. Water Ca-pacity ^ 





■ Held by 

capillarity 


Total 
water 


Excess of total 
over capillarity 


Sand 

Yellow-gray silt loam ." 


per cent 

27.80 
45.42 
48.31 
60.04 
66.66 
60.00 


per cent 

29.23 
■48.88 
52.10 
64.56 
69.32 
64.49 


per cent 

1.43 
3.46 


Yellow silt loam ■ 


3.79 


Brown silt loam 


4.52 


Black clay loam 


2.66 


Palouse volcanic ash soil 


4.49 







14 



210 



SOIL PHYSICS AND MANAGEMENT 



Amount of Water Moved by Capillarity. — The many experi- 
ments made indicate the movement of large amounts of water by 
surface tension. King used a fine sand taken from the subsoil and 
a clay loam in cylinders four feet high, each with a section equiva- 
lent to one square loot. The soils were completely saturated and 
the cylinders were placed so that the water level was one foot below 
the surface. A strong current of air was passed over the surface 
for eight days and the evaporation determined. The same thing 
was done with the water level at two, three, and four feet below the 
surface. 



Water Evaporated Daily 


Per Square Foot icith th 
Distances Below the Surface 


' Water Level at Different 

10 


Kind of soil 


One foot 


Two feet 


Three feet 


Four feet 


Fine sand 

Clay loam 


pou7ids 

2.37 
2.05 


pounds 

2.07 
1.62 


pounds 

1.23 
1.00 


pounds 

0.91 
0.90 







These results show that the amount of water raised four feet 
was equivalent to one inch of rain in five and one-half days. From 
such experiments the impression is given that capillarity is the 
great factor in bringing water to the crop. It does play a large part, 
but the conditions in the above experiment were much more favor- 
able than are ordinarily fomid in the field. The water rose from a 
free-water surface and the artificial breeze increased evaporation 
enormously. Capillary movement is extremely slow through clay 
loam, and it is very likely that the water evaporated from that soil 
when the water table was 36 or 48 inches below the surface was not 
obtained from the water table, but from the reserve in the soil. It 
takes more than eight days, as seen in the table, page 207, for water 
to be carried 48 inches or even 36 inches in height. The results are 
without doubt much higher than would be obtained under normal 
field conditions. In regard to capillary movement, Eotmistrov.^'^ 
of Russia, says. " As regards the mechanical raising of water, how- 
ever, by capillary action, it may be assumed that the limit from 
which water can make its way upward lies much higher than the 
limit accessible to- roots. All the data at my command regarding 
moisture in the soil of the Odessa experimental field point only to 
one conclusion, namely, that water percolating beyond a depth of 
40 to 50 centimeters (16 to 30 inches) does not return to the surface 
except by way of roots." 



CAPILLARY WATER 



211 



The evaporation from the lysimeters or draiiK. gages at Roth- 
amsted, England, from bare soil at depths of 20 inches and 60 
inches, shows an excess of 0.11 of an inch per annum for the deeper 
soil mass as an average for 34 years. This represents the water 
brought to the surface from the 40 inches of subsoil of the deeper 
gage, and amounts to only 13 tons per acre per annum, or not suffi- 
cient to grow more than one-half bushel of wheat. This indicates 
that a very small amount of water is brought from a depth greater 
than 20 inches by capillarity in a clay loam soil. 



Rainfall and Evaporation at Rothamsted, England,^''- Average for 34 Years, 

1871 to 1904 



Rainfall, 
inches 



Evaporation (or retained by soil) 



20 inches 



40 inches 



60 inches 



January . . . 
February . . 

March 

April 

May 

June 

July 

August . . . . 
September . 
October. . . 
November . 
December . 



Total per year . 



2.32 
1.97 
1.83 
1.89 
2.11 
2.36 
2.73 
2.67 
2.52 
3.20 
2.86 
2.52 



28.98 



0.50 
0.55 
0.96 
1.39 
1.62 
1.73 
2.04 
2.05 
1.64 
1.35 
0.75 
0.50 



15.08 



0.27 
0.40 
0.81 
1.32 
1.56 
1.71 
2.03 
2.05 
1.69 
1.36 
0.68 
0.37 



14.25 



0.36 
0.49 
0.88 
1.36 
1.61 
1.74 
2.08 
2.09 
1.76 
1.52 
0.82 
0.48 



15.19 



Results for maximum and minimum rainfall 



Maximum (1903) . 
Minimum (1898) . 



38.69 
20.49 



15.21 
13.17 



15.09 
12.59 



14.46 
12.80 



The Capillary Pull of Soils. — It is quite important to be able 
to measure this capillary force for different soils. A method for 
doing this has been devised by Lynde and Dupre. It consists of 
placing the soil in a funnel on a cotton cloth filter that is con- 
nected with a water column by means of a wick. The water column 
rests upon a column of mercury, the lower end of which is in a 
vessel of mercury. As the water evaporates from the surface of the 
soil the water in the tube rises and with it the mercury. The height 
of the mercury represents the pull. The capillary lift is quite large 



212 



SOIL PHYSICS AND MANAGEMENT 



in fine-grained soils, as shown in the next table, and would be suffi- 
cient to sustain a column of water of the height given in the third 
column. 

The Capillary Lift of Soil Constituents " 



Soil constituent 



Diameter of grains 



Height of HzO 



Medium sand. 

Fine sand 

Very fine sand 

Silt 

Clay 



.5 -.25 
.25 -.1 
.1 -.05 
.05 -.005 
.005 



feet 

.98 

1.78 

4.05 

9.99 

26.80 



Osmosis in Soils. — Lynde and Dupre ^* have demonstrated 
that soils containing fine particles act as semi-permeable membranes, 
probably producing only a fractional part of the pressure of a mem- 
brane. Movement of this kind takes place when a difference in 
concentration of solutions exists in adjacent soil masses. The direc- 
tion of movement is toward the point or zone of greatest concentra- 
tion. The osmosis is increased by a higher temperature, so that the 
movement is greater in summer than winter. 

King ^^ has found that manure incorporated with soil caused a 
rise of water into the upper three feet of soil, due to a stronger solu- 
tion and greater osmotic pressure. Fertilizers when applied to a 
soil dissolve and cause a greater concentration of the soil solution 
as well as a gTcater surface tension, with the result that water is 
drawn to the surface. It is probably true that tillage and the appli- 
cation of lime, both of which may aid bacterial action in developing 
plant food and thus producing stronger soil solutions, may promote 
better surface moisture conditions. 

Use of Capillary Water. — Capillary water is the form used by 
plants in their growth. Even in the most severe drouths plants 
cannot extract all of the film moisture. The common crops may 
use some gravitational water, but only to a very slight extent. Eice 
and cranberries are naturally adapted to growth in a very wet or 
even saturated soil. The amount of water in a soil for best growth 
varies within rather wide limits, but our common crops make best 
growth when soils contain from -40 to 60 per cent of their total 
moisture capacity. This is the optimum water content. 

Wilting Coefficient.^® — The moisture content of the soil at 



CAPILLARY WATER 



213 



which the plant wilts permanently or at which it cannot maintain 
its rigidity is the vAlting coefficient. This point does not vary a 
great deal with different plants, not often over three per cent and 
usually within 1.5 per cent. It, however, varies widely with different 
soils. The work of Briggs and Shantz shows that it is approxi- 
mately one and one-half (1.-17) times that of the hygroscopic coeffi- 
cient. It represents the lower limit of available moisture. In 
sands and light sandy loams in which the hygroscopic coefficient is 
very low the wilting coefficient is also low. In clay soils whose 
hygroscopic coefficient varies from 12 to 20 per cent the wilting 
coefficient is from 18 to 30 per cent, while in muck and jjeat soils 
it may run as high as 70 per cent. The wilting coefficient of the 
same soil is a constant that may be used in the determination of 
other constants, such as the hygroscopic coefficient and water-hold- 
ing capacity. 

The wilting coefficient is determined experimentally, but may 
also be found indirectly from other soil constants to which it sus- 
tains a definite relation. The following formula3 may be used : 

/ \ Ttr-ix- r^ m ■ J. Molsture equivalent 

(a) Wilting Coefficient = —~ 

l.o4 

(b) Wilting Coefficient = H ygroscopic Coefficient 

U.Oo 

(c) Wilting Coefficient = Moisture holding capacity 

(d) Wilting Coefficient = 0.01 sands + 0.12 silt -|- 0.57 clay 

The probable errors have been omitted from these formulse. 
Wilting Coefficients of Various Soils for Different Plants " 



Coarse 
sand 



Fine 
sand 



Sandy 
loam 



Loam 



Clay 
loam 



Corn 

Sorghum 

Wheat (Kubanka) . . . . 

Oats 

Barley . . 

Rye 

Rice (Japan) 

Squash 

Pea (Canada) 

Vetch 

Tomato 

Clover (red) 

Moisture equivalent 



1.07 

.95 

.88 

1.01 

1.04 

.91 

.96 

1.21 

1.02 

1.22 

1.11 

1.00 



3.4 
3.3 
3.3 
3.1 
2.9 
2.9 
2.7 
2.6 
3.3 
2.4 
3.3 



6.6 
5.8 
6.3 
6.1 
6.2 
5.9 
5.6 
6.4 
6.9 
6.1 
6.9 



10.2 

9.7 
10.3 
10.5 
10.5 

9.6 
10.1 

9.4 
12.4 

9.7 
11.7 
10.7 



15.5 
13.9 
14.5 
14.9 
14.2 
14.4 
13.1 
15.1 
16.6 
14.7 
15.3 



1.55 



5.5 



12.0 



18.9 



27.4 



214 



SOIL PHYSICS AND MANAGEMENT 



Available Moisture. — The non-available moisture is that per 
cent found in soils when permanent wilting occurs. It is possible 
that a small amount of this may be slowly available but insufficient 
for rapid or even normal growth. It is supplied to the plant much 
too slowly. When the capillary force equals the osmotic pressure 

j 1 Wali^r cf /iydrafion 

Wafer Free far /oo'C.) 



Unavaitabk 
Moisture 



Avai/abte i 
Moisture 



Unavai/ab/e 
Moisture 



tty^roscopic Coefficient 

Wiftinq Coefficient 

Moisture £c^iyo/ent 



Optimum Moisture Content 
for Ordinary Crops 



Moisture Motdina Capacity 



Comptete/y Saturated 



Fig. 94. 



-Diagram showing the relation of different forms of moisture to the available and 
unavailable moisture of soils. 



or force of the- plant the water may be said to be non-available. 
The difference between the wilting coefficient and the maximum 
capillary capacity gives the maximum amount of available water. 
Somewhere between these lies the critical or optimum water con- 
tent. Under held conditions the diiference between the amount of 



CAPILLARY WATER 215 

moisture contained and tlie wilting coefficient will give the avail- 
able moisture. A small amount of gravitational moisture may be 
used by plants. Ordinary plants live but make little growth when 
the soil is saturated. The diagram (Fig. 94) shows the relation of 
the soil constants and the different forms of moisture. 

QUESTIONS 

1. How does capillary moisture differ from liygroscoijic? 

2. Give law governing height. 

3. What causes the film on a water surface? 

4. Under what conditions will the film exert pressure? 

5. If the tension of water film is 73.9 dynes per square centimeter, what 

pressure will the lilm exert if the radius of curvature is 2.5 mm.? 

6. Explain the movement of moisture from one soil particle to another. 

Illustrate. 

7. How is moisture held in soil columns? Why is the film thicker on 

the lower particles? 
8i. What effect does fineness of particles have on capillary pull? 
9. What determines the height to which water will rise in soils? 

10. Why should a clay with a higher moisture content than a sand soil 

extract moisture from the latter when in close contact with it? 

11. What is the moisture equivalent of soils? 

12. Why should clay have such a high moisture equivalent compared with 

other soils? 

13. Find the moisture equivalent if the hygroscopic coefficient is 6.3 per cent. 

14. What determines tlie rapidity of capillary movement? 

15. What is the significance of the experiment with the clod? 

16. What effect does capillary movement have on root development? 

17. Give King's experiment with the covered soils. 

18. Define viscosity. What effect on surface tension does it have? On 

capillary movement? 

19. What effect does temperature have on capillary movement? Why? 

20. What effect do mineral substances in solution have upon tension ? 

Organic substances? 

21. What effect will an application of manure have on surface tension? 

22. Why does water rise faster in jnedium- than fine-grained soils ? 

23. Compare columns 1, 3, and 5 in the table on page 207 and explain dif- 

ferences. 

24. Compare 0, 10, 11, and 12 and explain differences. 

25. From the standpoint of capillary movement, is organic matter desirable 

in soils? 

26. How is the maximum capillarv capacity of soils determined? 

27. What about the delivery of large amounts of water by capillarity for 

crops ? 
?8. Give the conclusions reached from the drain gages at Rothamsted. 

29. Describe the method of determining capillary pull of soils. 

30. Will water rise 26.8 feet l""a-h in clav? 

31. What part does osmosis nlav in moisture movement? 

32. Give uses of capillary moisture. 

33. What is the wilting coeflRcient? 

34. If the hygroscopic coefficient is 6.2 per cent, what is the wilting co- 

efficient? 

35. What is meant by available moisture? 



210 .^oii rii\\^u'8 A\p ma\ac;i:mi;n r 

;U1. How do dilVorom soils ooiuparo in tho amount of avaiUiMo moisture? 
ST. A soil in tho tioUl iout<uns ^ti.o per ivnt of n\oistmo and tho hygro- 

sa^pio oiH<thoio»»t is H.o pov oont^ How muoh availablo moisturo does 

tho soil oontain? 

REFERENCES 

' lUi,i;>;>i. L. .K. Youvbook. l\ 8. l>. A.. 180S. p. 30l>. 

' Uri>i>is, I., .'.. and Mol-ano. J. \V.. The \loistnro Kquivalonts of Soils. 

Unllotin 4o, lUuoau of Soils, l". S. D. A., 1007. 
'^Kii\i;. K. U.. Wisconsin Station, Tth Ann. Kopvnt, p. 144. 
'Smithsonian riivsioal TahU^s, ISSUi, p. KU>. 
» Kin^ii. K. U.. Physios of -V^rioviltuiv. ItHU. p. 170. 

* Inpublishod data. Soil Tlusios IMvision, rnivovsity of Illinois, 
M.Yon. l\ L.. and Kippin. K. t\. Soils. UH>!>. p. U>0. ' 

* Kai'i'akor. I*. K., Journal of vV^rioultvual Kosoaroh. N'ol. 4. No. 'J, pp. 

187 to ll>-\ 

* rnpuWishiHl data. Soil Phvsios Division. I'nivor^itv of Illinois. 
** Kin^. V\ U.. Wisvvusiin Station. 7th Ann. Ivoport, p. l.M. 

" Kotn\istiw, V. 1%.. Naturo of Orovight .Vovvrdinj; to the Kvidenoe of the 

tVU^*s<> K^xperimont Station. Kussia. Knglish tslition. lOl.'i, 
" Hall. -V. P.. The IVok of tho Kothamstixl Kxporitnonts. llHVv p. :iS. 
" l.vndo. O. .1.. and Dupro. H. A.. Jour. An\. Soo. Airron.. Vol. .">. No. i, l;M;>. 

'p. 111. 
" l.ynde. C .V.. aiul lottos. F, \\ .. rnntHHlinji^i Am. StH". Ajrnm., \"ol. 4. pp. 
I0:i-l:!:2. Lvndo. (.\ 1.. and Pupr*^. H. A.. Jour. Am. 8ih\ -\srron.. Vol. 
o. No, :i. VoV 7. Ni^. I and <>, 
** Kin^sr. K, II,. Physios of .Viivioultutv, 1007, p, 172, 

** Urijiji^. 1.. J,, and Shant/. 11, 1«, Pullotin 2;>0. Rureau of Plant Industry, 
I". S, 0, .v.. The Wilting;' CwtVioient for PitToront Plant* and Us In- 
dinvt IX^termination, 1012. p. 72. 
"Op, Cit., pp. 2t5-;^;5. 

General Reference — Brigjrs. 1., J,. Pullotiu 10, Pivisiou of Soils. I". S. 
P. A.. Mtvhauios c»t' Soil Moisture. 1S07. 



r'irAi"ri';i: x\'ir 



WATER OF SOILS 

III. GRAVITATIONAL WATER 

Cravita'I'ional vv';il(!r is that vvliidi may he roiiovcfl from tho 
8oi] \)y tliti force of gravity or draiii(;(l I'lom tin; soil iindor jiormal 
conditions. The possible amount <;!' the gravJtatioJiai \vat(;r is the 
difference between the water bebl by a soil at its maximum capil- 
lary capacity and at its maximum water capacity, when completely 
saturated, or when the air space is completely filled. 'J^bis amount 
varies with tl)c type of soil. 

The (Jetcrmiiiation of tlie gravitational water capacity of soils 
is very unsatisfactory. 'J'be amount (lc|)enf]s upon the height above 
the water tabic The gravitational water is the difference between 
the water contciit, whfn comfjletely saturated, ajid when only satis- 
fied with capillary watci'. This amount will vary, since the same soil 
will be satisfied by a smaller amount of capillary water the greater 
the distance a})Ove the water table. King shows the amount of 
water at different heights above tlie water table with sands of dif- 
ferent grades and two soils. 

Water at Different Heights Above the Water Table After Being Saturated awl 

Drained ^ 



Height above 
water table 


Sand No. 20 


Sand No. 60 


Sand No. 100 


Sandy loam 


Clay loam 


incheH 


per cent 


per cent 


■per cent 


per cent 


i per cent 


84-81 


.23 


.61 


3.93 


16.16 


' 21.16 


72-69 


1.18 


1.80 


4.94 


16.. 5.0 


31.05 


60-57 


1.83 


2.26 


6.77 


17..59 


31.21 


48-45 


2.03 


2.46 


10.50 


18.70 


31.99 


36-33 


2.31 


4.10 


14.95 


20.90 


32.45 


24-21 


3.42 


13.52 


18.92 


21.46 


?AAO 


12- 9 


16.08 


22.46 


22.68 


22.68 


35.97 


6- 3 


20.96 


22.88 


30.28 


27.69 


1 37.19 



Percolation. — The movement of gravitational water downward 

through the soil by the force of gravity is called percolation. It 
depends upon several factors. 

1. Physical Composition or Texture. — Tlie movement of 
water through the soil by the force of gravity varies directly as the 

217 



218 SOIL PHYSICS AND MANAGEMENT 

size of the pat'tieles and the pore spaces, but inversely as the total 
pore space or tlie porosity. Sinee tliese factors depend upon the 
size of the particles, the physical composition is the coutrolling 
factor in percolation. If a fine-grained soil has 50 per cent of pore 
space and a coarse-grained one has 33. it must follow that the pore 
spaces in the former must be intinitely more numerous and smaller 
than in the latter. If the average diameter of the particles of the 
tine-grained soil is O.iU mm. and of the other 1 mm., the number 
of pores for equal areas will be approximately 10,000 times more 
numerous in the tine than in the coarse, and consequently the resist- 
ance to the movement of the water would be much greater in the 
fine-grained soil or through the smaller pores. The nearer the par- 
ticles approach uniformity in size the more favorable the conditions 
for percolation. If various sized particles are present and of sim- 
ilar shapes the smaller ones may tend to clog the interspaces between 
the larger and may render the soil impervious. If the particles 
are very irregular in shape, regardless of size, the permeability of 
the soil may be increased. This is true of volcanic ash soils. The 
structure of the soil is an important factor in percolation. 

•.\ Granulation. — In the case of clays and other fine-grained 
soils the cementing of the soil particles into granules aids percola- 
tion. The large intei'spaces existing between the granules allow 
free movement. Even in soils with considerable anunints of sand 
percolation may be aided by granulation. Heavy soils devoid of 
granules are almost absolutely impervious. Such soils are puddled. 
They may be so naturally, or they may become so by some mechani- 
cal operation, such as plowing or tramping of stock when wet. 
This condition may be only temporary. 

Any substance that causes or aids granulation 'will increase per- 
meability and consequently percolation. The application of lime, 
chalk, marl, or limestone to clay soils is a well-known practice for 
producing better tilth. Clay soils are readily permeable to water 
only when their colloids are in a flocculated condition. 

3, Organic Matter. — A very favorable effect is produced upon 
the permeability of medium- and fine-grained soils by the incorpo- 
ration of organic matter, but in coarse-grained, sandy soils the eft'ect 
of organic matter is to retard percolation, a thing very desirable in 
such soils. In silt and clay soils the irregular fragments of unde- 
composed parts of plants impart a porosity helpful to the downward 
movement of water, while the humified material aids in the pro- 



GRAVITATIONAL WATER 219 

duction of cracks through its property of shrinkage as well as its 
effect on granuhition, botli favoring the movement of water. 

4. Viscosity.— Changes in temperature affect the viscosity or 
mobility of water to such an extent that it moves more readily under 
high than low temperatures. The effect of temperature on capil- 
lary movement was shown on page 204. King found that the 
amount of water flowing through soil at 9 degrees C. was 6.15 
grams per minute, and at 32.5 degrees it was 10.54 grams. Briggs 
explained this greater flow on the theory of lessened viscosity, and 
showed that while the ratio between the flows is 1.71, the ratio 
between the viscosities is 1.77. These correspond so closely that 
there is no doubt that his conclusion was right. Water will perco- 
late through soils faster in summer than winter. Water at 32 
degrees F. and at 70 degrees F. was alowed to flow from a milli- 
meter opening under tlie same pressure in each case. Twice as 
much water flowed out at 70 degrees as at 32 degrees. At 32 
degrees the water did not come out in a stream, but dropped rap- 
idly from the tube, while at 70 degrees it flowed in a steady stream. 

The viscosity is frequently aft'ected by substances dissolved in 
the soil water. Some substances increase while others decrease 
viscosity, as shown on page 206. In the case of organic substances 
in solution percolation may be aided by the lessened viscosity. 

5. Atmospheric Pressure.* — The changes in pressure of the 
atmosphere, with its expansion and contraction accompanying the 
" lows " and " highs," affect percolation to some extent. The 
decrease of pressure allows the air in the soil to expand, thus forcing 
out some of the water into the drainage channels. King ^ found 
the discharge from a spring to be 8 per cent greater with a falling 
than a rising barometer and a variation of 15 per cent in the flow of 
water from a tile under similar conditions. 

6. Shrinkage Cracks, — The movement of water by percolation 
is aided greatly by the cracks that are produced in clayey soils by 
shrinkage during periods of drouth. Tliese cracks do not fully close 
upon subsequent wetting and may thus leave passageways for 
water. This is very important in heavy soils. The burrows of 
animals, especially insects and earthworms, penetrate the soil in 
all directions and furnish a ready means for movement of water 
both laterally and vertically. The greatest amount of work done 
by earthworms is in heavy soils where percolation is naturally 
slowest. These animals are not abundant in acid soils and those 



220 



SOIL PHYSICS AND jNIANAGEMENT 



dotioiout in organic niaiter. C'raytish aid the downward movement 
o( water bv their burrows. 

T. Roots of plants penetrate the soil and hiter decay, leaving 
passageways throngh which water may pass quite readily. 

Lysimeters or drain gages have been used for determining the 
amount ot' percolation and evaporation. The longest and most 
interesting records have been obtained at Kothamsted. England, 
where records have been kept for 34 years. The gages consist of 
masses of mulisturbed soil of different depths enclosed' in cement 
tanks with drainage outlets for measnring the percolation. The 
soil is a tUnty clay loam or heavy loam and is kept free from all 
vciietation. 



Rainfall, Percolation and Etxiporation ' at Rothamsteil, England, Arerage for 
S4 Yec^, 1S71 to 1904 





Months 


Kaiit- 
fall 


Pert?olation through 
soil 


Per cent ot" r.iiufall 
porcol.'itinp through soil 




inches 


20 
inches 


40 
inches 


l>0 
inches 


20 
inches 


40 
inches 


(50 
inches 


,lanii;\rv. . 




2.32 1.82 
1.97 1.42 

i.s;^ 0.S7 

I.S9 0.50 
2. 1 1 0.49 
2.30 0.03 
2.73 0.09 
2.67 0.02 
2.52 O.SS 
3.20 l.So 
2.86 2.11 
2.52 1 2.02 


2.05 

1.57 
1.02 
0.57 
0.55 
0.05 
0.70 
0.02 
0.S3 
1.84 
2.18 
2.15 


1.96 

1.48 
0.95 
0.5;^ 
0.50 
0.02 
0.05 
0.58 
0.76 
1.6S 
2.04 
2.04 


78.5 

72.2 
47.6 
26.5 
23.2 
24.0 


88.4 
80.0 
55.6 
30.0 
26.1 
27.6 


84.5 


Fobruarv . 




75.2 
52 


April 

May 




28.0 
23.6 


Jiuio 


26.3 


Jvilv 


25.3 ! 25.6 
23.2 ! 23.2 
35.0 ! 32.8 


23.8 




21.7 


Soptombor 
iV'tobor 




30.0 




57.8 


57.5 


52.5 


N'ovoiubor 




76.7 
80.3 


76.3 1 72.4 


D<?06iwber 




85.4 81.0 






Totftl p6i" ^'^-*n' 


28.98 j 13.90 


14.73 


13.79 


48.2 1 51.0 i 4S.0 




*' 






Results for Years 


of Maximtttn 


and Mi 


mmttm 


RainfaU 




(^1903^ 


38.69 23.48 
20.49 7.32 


23.60 
7.90 


24.23 
7.69 


60.7 
35.7 


61.0 
38.5 


63.0 




(1S98) 


37.6 













It Avill be noted from the above table that the amount of perco- 
lation varies but little for the ditferent depths of soil. The average 
percolation for the '.^O-inch depth was 13.90 inches, while for the iHV 
inch it was lo.T9 inches. This shows that only 0.11 inch more water 
was ivtained by the deeper ^oil. 



GRAVITATIONAL WATER 



221 



Water Draining from Eight Feet of Saturated Sands. 

Soil,* King 



Percentage Based on Dry 



Time of percolation 



1 hour 
1 day. 
3 days 
9 days 
268 days 



Meshes per inch of sieves 



20-40 



9.6 
13.8 

14.5 
15.3 
16.4 



60-80 



6.6 
11.8 
12.5 
12:9 
13.6 



100 

1.4 
6.3 
7.5 
8.4 
9.3 



The table shows the amount of water draining from eight feet 
of saturated sand soil in 3G8 days. The drainage, of course, was not 
continuous during this time^ but varied with conditions of tem- 
perature and atmospheric pressure. During the last 259 days of 
intermittent drainage the sand lost from 6.56 to 9.15 pounds of 
water per square foot, or from 1.2 to nearly 1.8 inches of water. 
Percolation is only possible when the air can enter the soil, hence a 
slight rain falling on the surface may retard or entirely stop perco- 
lation by sealing the surface so that the air cannot get out. This 
has been observed at the TJothamstod drain gages. 

QUESTIONS 

1. Define gravitational water. 

2. W'liat is tlie maximum water capacity? 

3. Which may have the greater gravitational water capacity, sand or clay? 

4. Define water table. 

.5. How does the movement of water through soil vary? 

6. Compare the number of pores in a sand soil, particles 0.05 mm., with a 

silt soil, particles 0.05 mm. 

7. What about the ell'ect of shape and size of particles in the same soil 

on percolation ? 

8. What part does granulation play in percolation? 

9. Give the effects of organic matter on percolation. 

10. Explain the effect of viscosity on percolation. 

11. What things affect the viscosity of water? 

12. Explain variations caused by changes in atmospheric pressure. 

13. What other factors aid percolation? 

14. Describe the Rothamsted drain gages. 

15. What conclusions may be drawn from the results ? 

16. Give King's experiment regarding drainage from sands. 

REFERENCES 
^King, F. H., Physics of Agriculture, 1907, p. 134. 
='King, F. H., The Soil, 1907, p. 180. 

^Hall, A. D., The Book of the Rothamsted Experiments, 1905, p. 23. 
*King, F. H., Wisconsin Station, 11th Ann. Report, p. 285. 

General References — King. F. H., Principles and Conditions of the 
Movements of Ground Water. U. S. Geol. Survey, 19th Ann. Report, Part 
II, 1897-98, pp. (J7-20(i. 



riiAr'FKK will 

CONTROL OF MOISTURE 
I. DRAINAGE 

Yeky few places on tho earth's^ suvfaeo have an\plo rainfall so 
Avoll distrilnitod that no attention nood be given to the eontrol ot' 
moistnre. In many humid and snperhumid areas the great prob- 
lem is disposing of the exeess ot* water, while in semi-arid regions 
it is to eonserve the rainfall for the erop. while in the still drier 
regions irrigation is the all-absorbing problem. Even in the humid 
areas some seasons are so drv that the utmost eare must he exereised 
to hold the moisture for the erop. 

Removal of Excess of Water. — Drainage. — The average soil 
has about oO per eeut of pore space. A waterlogged soil is one 
having the pore space tilled with water. It becomes necessary to 
remove this excess of water so that the food-prixlucing bacteria 
and the rix^ts of plants may be able to secure oxygen. The water 
table in the soil must be from three to four feet below the sur- 
face, sutlicieui to give nunn for the development of large root 
systems. If it is above this it mnst be lowered by drainage. Be- 
sides the lowering of the water table many other benetits are de- 
rived from drainage (Fig. 95). 

(a") Orainage gives stabiliti/ to the soil. Ordii\avily whei\ a 
heavy weight is applied to a very wet soil the particles are pushed 
to one side, the excess of water weakens the cementing material 
of the granules aiut acts somewhat as a lubricant to the particles. 
This movement is very injurious to the tilth of the soil, since it 
breaks down the granules, prodircing a puddled condition. This is 
very likely to occur in any soil, but more particularly in a heavy 
one. Freezing and thawing or wetting and drying may overcome 
in time the eomiition produced if the soil is drained. Great dam- 
age is sometimes done by pasturing wet soils during late winter 
and early spring. 

(b) Soils (.\nitaining an excess of water ai*e rarely in good 
ph^'sical coiiditioit. Granulafion is prcxluced by alternate wetting 
and drying, and a soil that is saturateil practically all of the time 
cannot be subjected to these beneficial conditions. Freezing and 



DRAINAGE 



223 



thcLwin(j is also aiiotliei' means loi' producing graiiuJatioii, if Uk; 
right amouiii oi' water is presuiil. J I' tliere is an excess oJ' water tlie 
e/rect of l'r(!eziiig and thawing is to hrcsak down tix; granules. Jn- 
slcad of j)foducing good lilth a. '' runny/' piiddhjd condition results. 
Tlie soiJ oi' a pond where water has stood (iuring the winter will 
be run together very badly by spring and heconie quite compact. 

(c) It seems almost paradoxical that the removal of llu; excess 
of water should increas& th,e available moisture for plants, yet it is 
true. Lowering the water table to a depth of lhre(! or four feet 
enables plant roots to develop in a larger area than is otherwise 












\i 




'A'\ $^x 



Fio. 95. — The difference in Hf-'rmination aiiil trriAvth <jii midraiiiccl soil CA) and dmiin-d 
(B) Hi)il. Same kind of soil and the same kind and number of m;ed« W(;re planted. (Lniverhity 
of Illinois.) 

possible, since plant roots do not penetrate a waterlogged soil. 
This will give them a chance to secure the water from a deptli of 
three feet or more where otherwise they would be limited to one 
or two feet. Capillary water, only, is used by plants, and drainage 
increases the volume of soil that contains this form of moisture. 

(d) The removal of tlie excess of water aids aeration, since the 
water is replaced by air. About 50 per cent of the volume of the 
soil as it ordinarily exists is pore space, and about one-half of this 
should be occupied by air under ordinary conditions. This, in a 
waterloirored soil, would be filled with water. The optimum con- 
dition for plant growth is sufficient moisture for the use of the 



224 



8011. rHV8KS ANP MAX AO.KMKN r 



plant, but not so murh as to orowJ out tho o\vuvn. wluih is 
oqiiallv esissoiuial. 

(o) Tho 1 1' 1)1 p<m( tire ot' tho soil will bo raisod bv tho romoval 
of tho watov. siuoo tho i^pooitio boat of tho soil will bo lowor with 
less watoi\ If the spooitio heat of water is 1 ai\d that of soil is 
0.'^. thou a watorloii'gvHl soil having an apparent spooitio gravity lU' 
l.v and oO per oont of n\oisturo wonld have a spooitio heat of 0. Ui. 
or tho amount of hoat roquirod to vaiso tho tomporaturo of tho wot 
soil one degree wovild bo more than twioo as groat as for tlio dry 
soil. Anotl\ev faotor that atteots the tomporaturo is tho lowering 
of evaporation by drainage. Evaporation is a in^oling pnx'oss. and 
every poiuui of water evaporated from the snrfaiH^ of tho soil to- 
qnires IHUJ.U hoat units, and this will be takoit largely from tho 
soil, llemv wot soils aiv 'Mate" soils. Thoy may be tnins- 
formed into " early " ones by drainage ( Fig. J^'^") . 

Prainago lengthens tho gnnving season of oerrain soils, and 
may possibly permit a iH->mploto ohango of orops. Conditions are 
moiv favorable for biologioal aotivity in the drained soil beoauso 
of tho inoivase in temperatuiv and of hotter aeration. King found 
that well-draii\od sandy loam had a tempoTatnre of 00.5 doarrees F., 
while in an nndrained blaok marsh the temporat\iro was o4 degrees 
at the Siimo depth. , ■ 

Experiments eomlnoted with tra\"s filled with the same soil, 
one of whioh was drained while the other was not. show ditToroinvs 
as given in the table. 

Effwt (if Dmitwgf on Ttmimatwre of a SoU ' — Degrms Fahretkheit 





Thorniauuner 1 inch 


Thwimuneter S inrhi}i$ 


Thernunueter 4 inches 


Ti«»e 


bolow s 


urfa<.-« 


below 


surface 


below svjrface 




1 Dr»in«>d 


Vndnuued 


Drained 


Vndrsuned 


Drained 


Undraincd 


A.M. 


4t^.7 


4,=^.0 


49.0 


47.2 


52..T 


50.0 


S \.M- 


.x^ 


o2.:^ 


o;^.o 


oO.o 


ol.O 


49.5 


10 A.M. 


To.O 


t^TO 


iHv.'i 


tuo 


o< .o 


54.0 


12 M. 


So.n 


r,i.o 


77 


68.0 


07 


02.0 


1 r.M. 


87.0 


TS.v^ 


70.4 


70.7 


70.0 


ixS.l 


2 r.M. 


S4.0 


72.0 


SI 


72 


74.2 


l^.O 


3 P.M.. 


Sl.O 


70.0 


so.o 


71 


70.O 


70.5 


4 P.M. 


Ttvt 


iM.l 


77.0 


(\^.o 


7t>.S 


70..^ 


5 P.M. 


71.2 


IvvS 


74.2 


IV.O 


7o.4 


70.0 


6 P.M. 


l>8.0 

1 


li2.0 


72.1 


Iv^.O 


74.0 


l^^.O 



It will Iv noted that the greatest ditferenoe betwotMi the drained 
and nndraintnl soil at one inoh in depth was lo.T degrees, at two 
inohtvs 9 degrws, and at 4 inehes 6.^ desrrees. 



DRAINAGE 



225 



{{') The removal df i\\r. (excess of walcr ri'oiii l\\r. soil iiici'(;iis(!.s 
(Ircoiii/Kisilioii and iiUri/inil ion, processes lUH-essary I'oi' Uio growth 
of plants. As a, t^cneraJ rule, ilie mosses niid grasses of swamps 
lia\(' ileeomposeil to a wvy slight, extent only, heeause of the oxeesfl 
of moisture wliieli pi'events the access ol" oxygcMi. Druinjige allows 
aeration and the pi'ocess ol' nit riticat ion may then take phK^e. 

(g) " II ('tiviiuj " of soil or crops on medium- to (Ine-grained 
soils is diminished or almost; entirely ])revenlcd hy the ivmoval 
of the water. When a wet soil IVoo'/es it expands in th(! direction 
of least resislanci\ which is upward, and IIh; ci'op, whatever it is, 




I''i(i. 'Ji;. - Pipe lic:ivccl iiraily f, iiiclicH (Iminn wiiilcr of 1 '.M Ti- I 'J Hi. 

is pushed along with it. 'This process l)(M'ng repeated ov(!r and 
over may " heave" a crop out of the soil entirely, as in the case of 
young alfalfa, elovei- or wheat. If the soil is drained, the expan- 
sion of the smaller amount of water in freezing will he taken care 
of in the pore spaces of the soil without expanding upward to 
such great extent. Figure 9(1 shows the heaving of a gas pipe 
stake during one winter, and figure !)7 shows tlu; heaving of 
alfalfa in a poorly drained soil. Where tight suhsoils ar(> |)reseiit 
the danger of heaving is very great, so that it is practically im- 
possihle to grow alfalfa and clover. 
15 



226 SOIL rU\SK;> AND MANACKMllN T 

H^h'i The etTiVtiYonct^^ of ihowxi^jjh drainairo in pirrenimg 
«^nK<fH>w hj\* K\n\ olvisorvod in nianv in5*iaiu\'^» Inu lUis point is dis- 
oussihI under the subjivl of erx^ion. 

(i) Oraiuji^v i;? one of the luo^st effeetive moaiis? for roiuoving 
«Ikali froiu kiul under irrig;\tiou, and thus? prevoivtin^ its *^ risse " 
and v\>n!*o<\uont injury to orv^jv^ It, in ^Hugunetion \vit)\ tUHxling. 
i!>also an ottoi'tivo niothinl for rtvlaiuiin^ laaul that oontaiuiJ j^o much 
alkali as to unulor it unprvvhiotivo. 

Types of Drainage, — 'IVo jivnoral tv^HV of dr?nna,i^^ havo Ixvn 
ei«jvlo>\\i, o|vu and tile drjtius, 

(a^ Open Drains. — In a crvat manv oases, the ojvn dnvin is 
an alvsolute uovvssitw be^aus^^ the large auuniut of water to be 
v^rrieil otT pnvhuU^? the iH^bilitv of usiii^ tHwennl drains at a 
reasouaWe oi^t, llemv thert^ will ah\"aA"s*l>e a large luimWr of 




Ft®. 9T. — At£»U» UvAS \vs^ vV-.v.v-"..;oiy kilkvi by l*avu^> Xvnn" ivvjs IviR* vm s^jrfaic*. 

Open drains, sueh as dre^lge ditches. In some eases open ditches 
jw neivssarv Kvause quicksand is ptvs^>ut which enters the drains 
thrvnigh the optniings Wtween the tiles and fills them so as to re- 
d\ict> their ofticiencv or even dog them entirely. In other places 
the fall or slope of the land is so slight that tile drains would W 
of veTY little nse and hence the open ditch lvcv>mes a ncivssity. 

A form of oj>en or surface drainage that is effei'tive and adaptevl 
to eertiiin tyjx^s of soil is that practicevl on soils with harvlpan or 
tight elay substrata. Swch soils occur in various }>arts of the 
v\>untry and the form of drainage adaptetl to them is that of dead 
furiv^ws or shallow ditches aUnit ^0 or ^o feet a\>art. These aw 
employed to a lar^ extent on aT<?as with tight clay sulvjoils, 

Therx^ aTv> so\~eral serious ohjectii>ns to o^x^n drains. They art? 
almo$t invariably expensix^ forms, l^ecause constant care is needed 



DRAINAGE 



227 



to keep the ditches open aud in good condition (Figs. 98, 99, lOOj. 
In a few years the fail may beeonne very uneven, due to more rapid 
eroHion at one place than at another. Obntru/itionH may get into 



yi'..'.)H 



Fro. '■)') 




Fio. 98. — The obotructionH in.U;rl<:T<; with th'; curr<;rit and cau»'; df;fl<;'rtion>i. ^fl. C, Wh'jekrr.; 
Fio, 99. — Ditoh gradually b<;ing fill':^] bj' hoil due to current being retarded b;.' graise. 




Fig. 1V>. — -^ nhuM':i'A ditch ofU;n seen in heavily wooded areae. (H. C. Wheeler. y 

the ditch which will eau.se deflections of the current and result in 
wearing away of the hank. . There is always a considerahle waste 
of land in connection with open drains even at the very be.st, and 



228 SOIL PHYSICS AND MANAGEMENT 

ail open ditch is always in the way. It interferes very seriously in 
iiiau}' cases with tillage of land, but one of the most serious ob- 
jections is the lack of physical benefit to the soil from open ditches 
in comparison with tile drains. This is principall}^ due to the 
fact that small open drains are never as deep as the corresponding 
tile drain and do not remove the water as completely. The growth 
of weeds and grass clogs the ditch and renders it less effective. 

(b) Tile Drains. — Since the object of drainage is to lower the 
water table, the tile should be amply large and the lines sufficiently 
close together and at such depth that the water may be removed 
before the crop suffers serious injury. If the tile is laid deep 
enough to lower the water table to only two feet beneath the sur- 
face on an average, a rain of two or three inches will raise it in- 
juriously near the surface, and if frequent rains follow the crop 
will be damaged in spite of the fact that the land is tiled. If 
the tile is too small this slow removal may permit very serious 



SuRfacs of Soil 




' 2 . . 3 

Fig. 101. — Showing the water table at a, with lines of tile at 1 and 3, and at bb, soon 
after the insertion of another line at 2 and later at b'h' . The slope of the water table between 
the lines of tile varies with the perviousness of the soil. • 

injury. If the water table is three feet beneath the surface and 
the foot of soil above it is two-thirds saturated, a rainfall of two 
inches will raise the water table a foot at least and damage to the 
crop may result. 

The topography of the water table in tile-drained land consists- 
of a series of ridges, with the crests about midway between the 
lines of tile. The height of these crests above the tile depends upon 
the texture and character of the soil strata, the distance between 
the lines, of tile and the amount of rainfall (Fig. 101). In laying 
tile the character of the soil should be taken into account and the 
lines placed close enough together so that the water table 'odll be 
lowered to at least 30 inches beneath the surface at its highest 
point. It must be remembered that the most of the water does not 
simply pass downward into the tile, but it must move laterally 
from two to five rods, depending upon the distance between the 
lines. The lateral movement is comparatively slow, so much so in 



DRAINAGE 229 

many soils that the crop is frequently damaged before the water 
table is lowered beyond the point of injury. The lines of tile 
should ])e laid closer in somewhat impervious soils than in pervious 
ones. In tight clay subsoils the tile drains should be not over four 
rods apart, and no doubt two rods would be better. 

Coarse-textured soils generally drain better than fine ones. An 
occasional tight stratum only a few inches thick may seriously in- 
terfere with drainage. In general, limestone soils drain better 
than strongly acid ones because of the granulation produced by the 
limestone. Heavy soils are especially aided by shrinkage and the 
formation of cracks to a depth of several feet which may not com- 
pletely close. Earthworms, crayfish and other animals do much 
to open up the soil for free movement of water, both laterally and 
vertically. 

QUESTIONS 

1. Wliat problems come up in the control of moisture? 

2. Define a waterlogged soil. \Miat objections to it? 

3. Explain some of the results of lack of stability in a soil. 

4. Why are permanently saturated soils usually in poor tilth? 

5. How does drainage afi'ect the available moisture? 
G. Explain how aeration is afl'ected by drainage. 

7. What is the effect of drainage on the specific heat of a soil? Why? 

8. ^^^ly does drainage affect evaporation ? 

9. How may drainage afi'ect crops and the length of growing season? 

10. Why are decomposition and nitrification necessary? 

11. How does drainage prevent heaving? 

12. Why does a tight subsoil cause heaving? 

13. Why are open drains necessary? 

14. How are tight clay soils usually drained? 

15. What are some objections to open ditches ? 

16. What precautions should be observed in tiling? Why? 

17. Upon what does the topography of the water table depend? 
IS. How low should the water table be? 

19. Why is lateral movement of water through soils so slow? 

20. What are some of the soil conditions that aid drainage? 

REFERENCE 

^Unpublished data, University of Illinois. 

General References. — Whitson, A. R., and Jones, E. R., Bulletin 146, 
Wisconsin Station, Drainage Conditions in Wisconsin, 1907. Fippin, E. 0., 
Bulletin 2.34, Cornell Station, Drainage in Xew York, 1908. Jeffery, J. A., 
Bulletin .56 (special), Michigan Station, Tile Drainage, 1911. Smith, A. 
G., Farmers' Bulletin 524, U. S. D. A., The Drainage of the Farm, 1913. 
Yarnell, D. L., Farmers' Bulletin 698, U. S. D. A., Trenching Machinerv 
for Tile Drains, 1915. Hills, J. L., .Jones, C. H., Williamson, C. G.. and 
Burdick, R. T., Bulletin 173, Vermont Station. Principles of Land Drain- 
age, 1913. Woodward, S. M., Bulletin 304, U. S. D. A., Land Drainage by 
Means of Pumps, 1915. Elliot, C. G.. Farmers' Bulletin 187, U. S. D. A., 
Drainage of Farm Lands, 1904. Kin?, F. H., Trrifration and Drainage, 
Part II, Revised Ed., 1909. Jeffery, J. A., Land Drainage, 1916. 



CONTROL OF MOISTURE 

II. TILLAGE 

Onk of the moans for I'outrolUng luoi^turo that is quite uni- 
vorsallv pnu'tiood is tlmt of tillago. It tiuds applioatiou in arid and 
somi-arid soot ions at all tinios and in humid and suporhuniid 
iVii'ions. niovo partioularlv in periods of drouth. .Vny form of 
implomont that stirs the soil, frvnn the erudost form of hoc to 
the i^KHverful tractor with its dozen plow?; and its harrows, will 
aov>omplisl\ the same objeet. 

Increasing the Moisture Capacity of Soils. — Probably one of 
the most im}H>rtaut faetors in supplying soils with sutVu-ient moist- 
un^ for owps is by inereasing their water holding eapaeity. This 
may be aivomplished by several uietluxls: 

(^a) By Tillage. — Soils fnnpiently Kvome so eompaet that t'Uey 
will not absorb water readily. heu(,v there will be a large rnu-otT 
and a eonsinpient loss not only of water but of soil material due 
to en^sivm. Only the water that is aWorlnxl can Ih^ of any benetit 
to en>ps. Henee it Kviunes verv ueivssary to put the soil in 
ivnditiou to aWorb as mueh A\"}Uer as ^H^ssible. This ean best be 
aeeon\plished by stirring the soil to ivnsiderable depth with some 
form of plow. The lM>st implement for this purpi^se is the evnn- 
mon mold Kvml plow. In plowing, the soil is not only inverted, 
but pulveri.:ed. and this is very Ivnetieial if the soil is in pn^per 
ivnditioi\ with ivspeet to moisture. To ii\eivase the storage eapaeity 
to the givatest extent plowing should l>e as divp as possible. The 
storage eaptieitv may easily l>e doubled by this meai\s and the soil 
put in vendition to absorb water readily so that very little runs off. 
This praetiiv is espooially advisable on rv^Uing land ai\d in semi- 
arid regions. 

(h> Compacting the Soil. — In the piwvi^ of plowing the soil 
is left tOi> hx^se for rt^itaining moisture to the highest degree, either 
agtjii\st |X»rv\>lation or evaporation, and in order to bring about 
prv^per venditions a eenain amount of innnpaeting is niwssary. 
This may be done by various implements, sueh as the spike-tix>th 
harnnv. the disk harrv>w. the rotary harrow, the cvrrug-jited rc»ller. 

230 



TILLAGE 2;il 

or the siilisiirracc pucker. The use ol' these iiiiph'tnontH closes Jiiiy 
lur^e Jiif sjjiiees that exist in (Ik; soil tliut would tend to iiienjuse 
either (naporiition or pereolai ion and hence renders tfie soil mueli 
nioi'c releii(iv(! of moisture lh;in il wouhl he ol hervvisi!. 

((■) Organic Matter. The water holding- enpneity of the soil 
ni;iv li<! largely iiierc;iscd llirou<r|i (he; addition of or;^;uiic niiitt(!r. 
'IMiis eonslituent ncls as a s|)on^(!, ahsorbinf^ lar<;(^ (juantities of 
water which are held against the i'orco ol" gravity. ("apillary 
nio\cnien( is rclarded, llius deeroasing surface evaporation. 

(d) Deep Rooting Crops. — 1'lie eU'eet of deej) rooting crops 
is somewhat similar lo deep plowin<^ or suhsoilinf^ (!Xce[)t that tli<; 
openings made hy I he roots hecomc j)artly lille(| with or<(anic 
niattiM', which in jtscdf is beneficial. The op(!nin<rs rurnish a 
passageway for wat(!r and air to greater de|)ths than any practi(;al 
tillage could do, lluis enlarging the; water reser\-oii'. The decay of 
the organi(; matter produces a somewhat granular condition in the 
(lee])er subsoil that ai(Js in the absor])tion and retention of moisture. 
Oi'teii the subsurface and subsoil become so coinpact that the water 
is |)revented froni percolatJJig through them to aJiy gr('at extent, 
and this permits the surface stratum to become saturated and then 
a large amount of run-oil' and evaporation must necessarily occur. 

Removing the Excess of Moisture by Tillage. — The re- 
nio\al of water by tillagi; is not often practiced and its applica- 
tion is \ryy limited, ^'et if a Jew inches of surface soil con- 
tains too much water this may be removed to some extent by 
tillage, which encouragc^s evaporation from the stirred soil, but 
the greatest care is necessary. Tlu; soil may be jdowed or culti- 
vated and left scjmewhat rough, thus giving it a chance to dry 
out. This may permit seeding earlier than if left in its orig- 
inal com))act condition. In certain soils rolling may be (d' benefit 
because of th(! (dl'ect it has in compacting the soil and facilitating 
capillary movement of moisture to the surface wh(;re it is evapo- 
rated. Freciuent cultivation may also have a similar effect ijr 
dryiirg out the cultivated soil, since every cultivation will bring to 
the surface? moist soil that will Ixfcome dry, and Ix^tter conditions 
for seeding may be pr-odnced in this way. '^Pfiis should rrot be 
practiced with soils that are easily puddled, l)ut may be advisable 
for sandy soils or those having an aburrdance of or'ranic matter. 

Decreasing Losses from Soils. — Water is lost from soils 
by percolation to depths below tlu; (;apillary limit by drainiage or 



232 SOIL PHYSICS AND MANAGEMENT 

percolation, bv transpiration from leaves of plants and by evapora- 
tion from the surface of the soil. 

(a) Decreasing Percolation. — The amount of percolation de- 
pends very largely on, the texture of the soil itself. As a general 
rule, the coarser the texture or the larger the air spaces the greater 
the amount of percolation. This, of course, may be modified by 
the amount of compaction and also by the organic-matter content. 
The amount of percolation depends, too, on the openness of the 
soil produced bv tillage as given above. Excessive percolation 
where it is due to coarseness of soil texture is very difficult to 
prevent. 

The incorporation of some water-retaining material such as 
clay or any of the tiner soil constituents or organic matter with 
the sand or gravel will aid in accomplishing the results desired. 
The former is an expensive process, but has been done on a small 
scale with excellent results. The use of organic matter is a 
more practical but somewhat slower process unless under condi- 
tions where abundant supplies of farm manure are at hand. Com- 
pacting is very beneficial in case of sandy soils, but must be care- 
fully done in the case of heavy soils. 

(b) Decreasing Transpiration from Plants. — All plants in 
their growth require enormous amounts of water, practically all 
of which must be secured from the soil. We have seen thiit from 
300 to 500 pounds of water are required for each pound of dry 
matter produced. This means that crops remove large quantities 
of water from the soil. 

The relative amount of water required may be reduced by an 
abundance of plant food provided through cultivation, rotation 
and fertilization. Weeds and other plants foreign to the crop 
should be destroyed to prevent them from depriving it of the 
moisture necessary for its growth. 

(c) Preventing Evaporation by Mulches. — A mulch is any 
material placed on or produced from the surface soil by tillage. 
Its object is to prevent evaporation. To be effective a mulch must 
be dry. Since moisture films pass very slowly into dry. loose soil, 
practically all of the moisture that is lost is by interstitial evapo- 
ration and diffusion through the mulch air to the atmosphere above. 
This diffusion takes place very slowly. 

The following table gives the results obtained bv Buckino-ham 



TILLAGE 



233 



with different depths of air-dr}' mulches, the soil used heing the 
Leonardtown loam : 

Loss of Water by Interstitial Evaporation and Diffusion Through Mulches of 
Varied Thickness of Leonardtown Loam ^ 



Depth of mulch 


Moisture lost 
per year 


Depth of mulch 


Moisture lost 
per year 


inches 
1 

2 


i7iches 

2.71 
1.60 


inches 

4 


inches 

0.95 
0.69 



With a 12-iiich mulch of Takoma lawn soil the loss of moisture 
amounted to one inch in six years. The amounts lost are so 
small that they need not be taken into account. Under field con- 
ditions a mulch is rarely ever perfect. There will be some places 
where capillarity is at work. Hence under field conditions labora- 
tory results are seldom attained, but they furnish principles to 
guide in farm practice. All mulches enclose air of high humidity, 
thus retarding or jDreventing evaporation from tlie moist soil be- 
neath. The dry layer prevents capillary movement to the surface 
and is made much more effective l)y its looseness. 

There are two kinds of mulches, artificial and soil mulches. 

(a) Artificial mulches are formed by the application of 
manure, straw, chaff, peat, leaves, sawdust and other materials 
to prevent evaporation. This method must necessarily 1)e very lim- 
ited in its application because of the expense attached and labor 
involved. Such mulches are, however, very effective. At the same 
time other ol)jects are accomplished, such as preventing the growth 
of weeds and adding plant food. Strawberries and bush fruits are 
sometimes mulched with straw, manure or leaves. " Straw " pota- 
toes are grown quite extensively on the deep loessial soils along the 
Mississippi riA^er. The potatoes are planted three or four inches 
deep in the soil. After the soil becomes warm and l)efore the 
potatoes come up they are covered with straw to a depth of six or 
eight inches. It keeps down the weeds, conserves moisture and 
furnishes some plant food which is leached rut of the straw into the 
soil. 

In Europe and other countries stones are placed upon the sur- 
face of the soil in hillside vineyards to conserve the moisture. 
Gravel is sometimes applied for the same purpose. 

(b) Soil mulches are by far the most practical and common 
means of conserving moisture. They are applicable to all climates 



234 



SOIL PHYSICS AND MANAGEMENT 



and conditions. Tlie soil mulch consists of a dry layer of soil, 
either loose or compact. The loose mulch is far more effective and 
common than the comi^act (Fig. 102). This latter results only 
after much moisture has been lost from the soil, and should not be 
depended upon. 

Some soils are self mulching to a certain extent. Sands, peats 
and highly granular soils are of this character. The best way of 
producing a soil mulch is by tillage, the kind of implement depend- 
ing upon the soil, its tilth and moisture content, and the kind and 
condition of the crop. 

Fineness of the Mulch. — Mulches may be made too fine to be 
of greatest value under all conditions. If fine- or medium-grained 

r ] 




Fig. 102. — A good method of conserving moisture. 

soils contain little organic matter, cultivation tends to produce a 
mulch of individual particles or a dust mulch, which, while it serves 
very well for preventing evaporation, yet serves equally well for 
preventing absorption of rainfall. Hence the first dash of a heavy 
shower causes these particles to run together and produce an almost 
impervious stratum. If the mulch is not so fine or is somewhat 
cloddy or granular this running together does not take place so 
readily and a much larger proportion of the rainfall will be ab- 
sorbed. This in arid regions becomes a very serious problem where 
it is desirable that all of the rainfall should be absorbed. Hence 
a mulch should not be made with an implement that reduces the 
soil to dust. 



TILLAGE 



235 



The Depth of the Mulch. — The deeper the mulch the more 
effective it is. King has shown ver}^ conclusively that evaporation 
is prevented to a very large extent by deeper mulches. The fol- 
lowing table gives his results : 



Effectiveness of Soil Mulches of Different Kinds and Depth 

100 Days 



2 — Water Lost in 







Mulch 


Mulch 


Mulch 


Mulch 




No mulch 


1 inch 


2 inches 


3 inches 


4 inches 






deep 


deep 


deep 


deep 


Black marsh soil: 












Tons per acre .... 


688.0 


355.0 


270.0 


256.4 


252.5 


Inches of water. . . 


5.193 


3.12 


2.384 


2.265 


2.230 


Per cent saved b.y 












mulches 




34.54 


54.08 


56.39 


57.06 


Sandy loam: 












Tons per acre . . 


741.5 


373.7 


339.3 


287.5 


315.4 * 


Inches of water 


6.548 


3.3 


2.996 


2.539 


2.785 


Per cent saved 












by mulches . . 




49.69 


54.24 


61.22 


57.47 


Virgin clay loam . 












Tons per acre . . 


2,414 


1,260 


979.7 


889.2 


883.9 


Inches of water 


21.31 


11.13 


8.652 


7.852 


7.805 


Per cent saved 












by mulches . . 




47.76 


59.38 


63.13 


63.34 



It will be noted from this table that the four-inch mulch was 
no more effective than the three-inch. 

Deep mulches are very effective in conserving moisture, but 
there are serious objections to their use where crops are grow- 
ing. The objections apply more directly to farming in humid 
than in semi-arid and arid regions. If in humid areas a mulch 
three or four inches deep is produced on a soil with an intertilled 
crop, serious root injury will occur which will materially decrease 
yields. Deep mulches are practical only on bare soils. The effec- 
tiveness of a mulch depends upon its looseness and dryness. A 
three-inch mulch means the loss of a large amount of water if it 
is to be effective to its full depth. To maintain a mulch of this 
depth more frequent cultivation is necessary than for shallow 
ones. Every cultivation turns under dry soil and brings moist soil 
to the surface, resulting in loss of moisture. Shallow mulches are 
easily maintained with a minimum of cultivation. In humid 
climates, if the crop is free from weeds, there is little necessity for 
cultivation of sands, sandy loams and silt loams. 

Besides the moisture lost from the mulch the plant food that 



230 SOIL PHYSICS AND .MANAGEMENT 

it eontaius is unavailable for llie use of the crop. If the muleh is 
three inches deep it means that about oue-lialf of the plowed soil, 
the most fertile part, has little value except for the conservation 
of moisture, and in humid climates this layer is of much greater 
value to the crop for the plant food it contains than for the moisture 
it conserves. 

Maintenance of the Mulch. — I'uder certain conditions the 
soil mulch may bo entirely destroyed or rendered much less elfee- 
tive by a shower, so that it becomes necessary to renew it. Tillage 
of some kind must be resorted to in order to reproduce it. After a 
light shower a harrow or weeder may be effective in renewing it. 

The ease with which a mulch may be maintained depends to a 
large extent upon the kind of soil. Sands and sandy loams respond 
readily to tiUage and the mulch is easy to produce. Soils contain- 
iug large amounts of organic matter are granular, and a loose, 
mellow surface mulch is maintained without dit!iculty. Hea"S"y 
soils, low in organic matter, present the greatest ditliculty. since 
they are likely to be cloddy and deficient in granulation. To pro- 
duce a good mulch in these soils by mechanical means alone is 
almost impossible. Anything that encourages flocculation will 
materially aid in the formation of mulches. 

The maintenance of a mulch is especially important in arid 
and semi-arid sections where so much depends upon the conserva- 
tion of moisture. Even with small grain the mulch is maintained 
by means of a light spike-tooth harrow or weeder until the grain 
by shading th.^ soil prevents excessive evaporation. 

QUESTIONS 

1. Wliat effect does compacting have? 

•2. What form of tiHage inoreji!?es the moisture eapacitr of soils to the 
greatest degree ? 

3. lloxv does orgjinio matter atTeot tlie water-holding capacity of soils? 

4. Explain the etVect of deep rooting crops on water capacity of soils. 

5. How may water In? removed by tillage? 

(>. How may excessive percolation be overcome or prevented? 

7. Explain how transpiratioii may be reduced. 

S. How much moisture is lost by interstitial evaporation and diffusion 

through the uuilch ? 
9. Whv is it impossible t<i have a perfect nmlch imder field conditions? 

10. How does the hvimid soil air of the mulch prevent evaporation? 

11. Detine an artificial nmlch. 

12. Give advantaires and disadvantages of its use. 

13. What is a soil mulch? 

14. How is it effective in retaining moisture? 



TILLAGE 237 

15. Give facts regarding fineness of mulches. 

16. What conclusion may be drawn from King's work as given in table on 

page '2,3,) '! 

17. What are some disadvantages of a three-inch mulch? 

18. How deep should the mulch be? 

19. How does a shower destroy a mulch? 

20. What ])art does texture play in the ease with which a miilch may be 

maintained ? 

21. How often should cultivation be done to maintain a mulch? 



REFERENCES 

> Buckingham, E., Bulletin 38, Bureau of Soils, U. S. D. A., Studies in the 

Movement of Soil Moisture, 1!)07, p. 17. 
UUng, F. H., Pliysics of Agriculture, 1907, p. ISO. 



OHArTEE XX 

CONTROL OF MOISTURE 

III. DKY-LAND AGRICULTURE 

The disitribution of rainfall over the surface of the earth is very 
irrogulaj, so that extensive areas are detieient in moisture and 
sjXH-ial cultural methods and sj>evial crops must be used. Many 
regions are so poorly supplied with moisture that crops cannot be 
grown, even under the l>est conditions, witliout irrigation. It will 
be well to consult the table, page 1S1>. on the animal precipitation 
on the earth's laud surface. The map. tigure Sl\. may Iv of further 
help in giving a convct idea as to the location of the humid and 
dry areas. 

From the table, page 1SJ\, it is seen that approximately Go per 
cent of the land area of the earth receives less than 30 inches of 
rainfall. AKnit Oo per cent receives less than 10 inches, while 40 
per cent has from 10 to 30 inches. In the Tnited States alone the 
dry-land region covers about one-half the entire area, and 1.135,000 
square miles of this is suitable for dry farming. Australia has 
aKuit tlie sjime amount, and extensive areas are found in Africa 
and Asia atul smaller ones in Euro|v and South America. 

Adaptation of a Region to Dry Farming. — In dry-land 
farming, while the amount of moisttire supplied by the rainfall 
is by far the most important factor, yet there are secondary 
ones that must be taken into cmisideratiou. These are frei^uently 
of sufficient importance to bring absolute failure if overlooked or 
neglected. These include evaporation and the character of the 
soil, which are of almost equal significance with the rainfall. 

(a'J Rainfall. — The adaptation of a region to dry farming de- 
pends u}x^n several factors, one of the principal ones being the 
amount of rainfall and its distribution througli the year (Fig. 
103 ). Dry farming is not practical with less than 10 inches of 
rainfall annually, but there are modifying factors. With this 
amount the moisture must l>e carefully stored and c-onserved for 
the oroi^s- The marifin is so narrow that a rear or two with a 



DRY-LAND AGRICULTURE 



239 



rainfall but 8lightly below tbo iiorniiil will result in failure. The 
distribution of this rainfall is quite important, althou<^h not so 




FlQ, 103. — -Types of rainfall over the dry-farm area of the United States. (After Henry) 




.-if? t:*-f,-<i'J'^ -^ -• 



FtG. 104. — Sage brush on land well adapted to dry farming. Utah. 

much so as in humid regions, since by practicing the best methods 
of conservation the moisture may be held in tlie soil. It is, how- 
ever, desirable to have the rainfall during the growing season. 



240 



SOU. niYSlCS ANn manackmknt 



m 




-0^' 





Pjq^ 1()5^ — A $rr$tw-4)>- soil i»o% wcU adapted to dry farmins (Dty Farmins. VVidtsoe. 
Courtesy Macnnllan Compaa>-.'» 



DRY-LAND AdUlOULTURK 



241 



(I)) Evaporation. — 'I'Ik^ iuinMiiil, (jF cvnporiiiion is owe of ilio 
factors iliiii <l(!t(;rr>iiiics in ii JiKiasuro tliu viiluc; of a ref^ioji for dry 
fiiniiiii;;', siiic(!, oilier tliiii^'-s hciiiig oqua], that placo is best adapicf] 
lo lliis priiciiec; wliicli Ikis I Ik; least evaporation ( l*'i^^ 101). \oi-lli 
Dakota with a rainfall of 115 inches has 31 inclKi.s of (ivjiporaiion 
from a frco-wat(!r surface diirin'^ the six Hwmuw.r months, wliilt! 
northern Texas wifh ;i, likf; rjiinfjill luis nn inches. Ii is very 
evident that ili(! former would he heiier adapiecl io dry farming. 



Rainfall an<l J'jvapoiaiionfrom a l''ri'j:-[Vati;r Surface '■ 



I'llKKiS 



Lost River, Idaho . . . 
Laramie, Wyoming . . 
Fort Duchesne, Utah 
St. GcorKo, L'tah. . . . 

Tucson, Arizona 

Mohave, (!aIil'ornia. . 
i'\)rt Yuma, Arizona. 



Annual 


Annual 


precipilution 


evaporation 


inches 


itichea 


8.47 


70 


9.81 


70 


6.49 


75 


0.40 


90 


n.74 


90 


4.97 


95 


2.84 


100 



(c) Soils. — The character of the soil is u[ nmcli importance, 
since majiy are entirely unfit for dry lai'inin*^, because of some 
peculiarity they possess which renders them incapable of retaining 
the; moisture necessary for crops. In selecting land for diy fjirni- 
iiig, it should not be an acid soil and should jieiiher be too (jpcn 
nor too impervious. Coarse-grained soils (Fig. 10.")) and ver'y fino 
grained ones arc equally ohjcc^iionahlc for this kind of agriculture. 
Layers 'of gravel or coarse sand or hardpan are serious obstacles, 
since in the one case the water passes beyond the range of capillarity 
and in the otlicT the storage reservoir is small and the moisture 
cannot percolate deep enough to be retained against evaporation. 
Medium-grained soils (Fig. 106) with uniform texture to a depth 
of eight or ton feet furnish best conditions. 

Water Requirements of Plants. — 'J'he amount of water used, 
by plants in arid regions is about one-half more than in hurnid 
regions. In Utah experiments were carried on for six years on 
fertile soils, and the conclusion is that an average of 750 pounds of 
water per pound of dry matter v/as required. 

Briggs and Shantz have made determinations of the moisture re-. 
16 



243 



SOIL rUVSlCS AND MANAGEMENT 



quiroiuouts ot" a lar^o number of plants. Tho ro5=uhs of their inves- 
tigations aiv given in the following- table: 

]\\Uirr Kicquinsd to Product One Pound t^' Dry Matter at Akron, CoU 



Millet 810 

JHM-jihvim » 322 ' 

Corn 3t)8 | 

8iu\tloww ftSii I 

WKoat ^ 513 ! 

l\\v?iut© " ;5S3 I 

Ivvrlov 534 j 

O.us.' 597 i 

Khv\ 905 



Potato 686 

Cowpea , 571 

Soybetui 744 

Sii^vr btvt ....... V 397 

l\t\i (."lover 7S9 

8w<vt oUn-vr 770 

.\ll':vlfrt S31 

Txiiuble wtHxi 2S7 

RvissiiUi thistle 336 



It will be stvn that the amount of water varies fiviu C8T to 905 
pounds jx^r pound ot* dry nu\tter. The average of the above is 550 
|Hnmds of water for eaeh pound of dry n\atter. Some erops are 
better adapted to dry land agrieultuiv than others beeause of the 
faet that they rv\]uiTe les^ water, while some have habits of growth 
that enable them to resist divutli. Many plants must bo aeolimated 
before Ivst results ean W obtained. 

Tlie I'tah Station found that oultivation lessened the amount of 
water ivquired. 

Poui¥U «^' WaiiiT R&gmr^i bi Proiiucz- a Pound ^/" lyry Matfer qf Com ' 



S.«u\dy IcKiun 

Cl.Hyio.Hm 

Cl.sy 

Typo not gi\-oi\. 



Not ewhivated 



603 

5^v5 

7iKi 

4ol 



Cultivated 



252 
42S 

265 



Loss of Water. — Kaiufall is lost from the soil in four different 
ways, namely : run-<^tf. ^H^rwlation. evapon\tion, and transpiration. 

(a") Run-off. — One of the t\?sentials of dry farn\ing is to pr^ 
vent loss of water through surfa«.v run-otf by putting the soil in con- 
dition to aWrb the rainfall. It is im^x^ssible to prevent some loss 
beeause of the torrential rains in arid regions. The soil should 
be kept in a hx^se vendition, so as to absorb water as rapidly as 
possible. 

(b"^ Percolation. — ^Tt is rarelT the case that there is so nnieh 
rainfall on soils well adapted to dry farming that water gets beyond 



DRV-LANI) A(JRI('IJL'njJ{,E 



243 



the range of eapilhiry ucUon. Tlicn^lon! h^ss \>y pcrccjliiiifjti is iii- 
Higiiiiicuiit. l\'n:()\id\(>\i inio IIk; upper noil luy(;rs iniiKt tiikc pluce 
very rapidly io (^licsck coinplcic sjiiiiniiion of ilu! siiffiicf! soil, ho- 
OHiise this would nssiill in mon; or l(;ss nin-oir. I^r lliiK purposo 
tlio loo,S(!r tfio Hoil tli(! hcLtcr. 




Fia. UH, 



A (lcM;p, iii(;iliijm-^ri,iin(;(| Hoil well adapted to dry luniiinj^. 
Vanning, Widtaoo. Courteay Macmillan Company.) 



Utati. (Dry 



(c) Evaporation. — Arid coiuJiiions are very well adapted to 
eva])(jration ol" water from the soil surfaee, due to the very low rela- 
tive humidity, the rarity of the atmosphere and the lar<(c' air move- 
ment takinoj plaee in arid ref^ion.s. This is the most serious source 
of loss. At Salt Lake City the relative humidity in summer is ahout 
35 per cent, while in humid regions the average is from 75 to 80 



2-i4 SOIL PHYSICS AND MANAGEINIENT 

per cent. As a general rule, the surface soils are drv iii arid regions, 
and this prevents, in a measure at least, a large loss of water, since 
the movement of water through dry soil is very slow. Very little 
evaporation takes place within the interstices of the soil itself, as 
has been shown by the table on page ^SS. Buckingham has shown 
that ,the amount of water lost by transfer upward along with the 
air in the process of aeration amounts to no more than one inch 
in six years. It. is true, however, that coarse soils lose a larger 
amount in this way than fine-grained ones, but the loss in either 
case may be neglected. 

(d) Transpiration. — All plants take water through the root 
hairs and a very large part of it is transpired througli the leaves. 
The amount of water used in this way constitutes practically all that 
is taken up. by the plant except that used in building up tissues, 
which generall}^ amounts to only a small fraction of the total 
amount. Transpiration varies with certain conditions, both of 
weather and soil, and in general the factors that affect evaporation 
from the soil affect transpiration from the plant (see page 188). 
This applies to plants growing in humid regions as well as under 
arid conditions. Transpiration varies inversely as the relative 
humidity, directly with temperature, with wind velocity and direct 
sunshine ; but it is decreased by a large amount of plant food mate- 
rial dissolved in the soil moisture. Arid conditions are especially 
favorable for transpiration. 

It must be remembered also that weeds, like Tiseful plants, 
transpire large amounts of water and may be one of the greatest 
sources of loss, unless the soil is kept free from them. Weeds have 
no place" on any farm, but more especially on a dry-land farm. 
Eotmistrov * says, " Weeds are the bitterest enemy of field culture 
and the best friend of drought." 

METHOD OF PREVE^TTIXG LOSS OF WATER 

In dr\--farm practice every means must be used for 'preventing 
loss of moisture. Other crop factors sink into insignificance in com- 
parison with this one. The moisture must be sufficient not only to 
start the crop, but there must be enough stored in the soil to mature 
it. The farmer knows that every pound of moisture taken from 
the soil that does not go through the crop vrill lessen the yield. 

The loss of moisture by evaporation is prevented to some extent 
by the crop itself. After the crop becomes large enough to shade 
the ground evaporation is greatly retarded. This is especially true 



DRY-LAND AGRICULTURE 



245 



of non-tilled crops. The air enclosed in masses of vegetation, such 
as wheat, oats, millet, clovers and similar crops, has a comparatively 
high humidit}^, so that evaporation from the soil is retarded and 
probabl}' almost entirely prevented during a large part of the day. 
It is a matter of common observation that the dew remains in 
heavy oats or wheat many hours after sun-up and is deposited again 
several hours before sunset. This will eifectivelv prevent much 
evaporation from the soil. While the humidity of the air in these 
crops of semi-arid regions would not be as high as in humid ones, 
yet the difference would be sufficient to lessen the evaporation. 

With tilled crops, shading aids to some extent, but the mulch 
IS the important factor. When the crop has grown to such size that 
the roots are well distributed through the soil, moisture has very 
little chance of reaching the surface because of the network of 
roots which are absorbing all moisture that comes within reach. 

Tillage. — The best means for preventing loss of water is by 
tillage, by which a mulch is maintained. Various experimenters 
have found that cultivation will save from 22 to 55 per cent of the 
water that would otherwise evaporate. 

(a) Depth of Tillage.— Tillage produces conditions in the soil 
that permit very slow capillary movement by forcing soil particles 
apart so that the films of water cannot pass freelv from one to 
another. As a general rule, the deeper the mulch the more effec- 
tive it IS in preventing evaporation. In arid regions the plowing 
IS one of the mfc^t fundamental operations, since'^it plavs two very 
important functions, first, in producing a loose mulch for retarding 
capillary movement, and, second, in forming a deep stratum for 
absorbing the rainfall and retaining it afterward. The Utah Sta- 
tion has conducted a number of experiments upon depth of plowing 
and the results show that eight to ten inches is the best depth"* 
When increases for greater depths are obtained they are usually 
too low to cover the additional expense. 

Yields of Wheat for Different Depths of Plowing. Utah Station.— Bushels 

Per Acre ^ 





Juab 
County 


Washing- 
ton County 


Tooele 
County 


Sevier 
County 


Plowing 8 inches deep 

Plov/ing 10 inches deep 

Plowing 1,5 inches deep . . 


23.3 
23.4 
16.9 

15.4 


11.6 
12.0 
15.2 

15.2 


14.7 
14.9 
14.8 

16.2 


5.3 

5.8 
6.8 


Plowing and subsoiling 18-20 inches 
deep 




6.4 



246 SOIL rPIYSlCS AND MANAGEMENT 



Moderately deep pUnving is vorv essential, sinee it prevents loss 
bv surfaee drainage. 

(b) Fall Plowing. — Summer or fall plowing is especially ad- 
vantageous because it permits the absorption of winter rains and 
snows, and if cultivation is then done as early as possible in the 
spring a large amount of moisture may be held in the soil for the 
use of the crop in the fall or the following season. If the plowing 
must be done in the spring it should be done as early as possible to 
catch the rains and hold what is already in the soil. 

The disk can be used to gwd advantage on either fall or spring 
plowing to produce deep mulches. Even on stubble the disk can 
be used to advantage as soon as the grain is removed. 1 f a crop is 
seeded in the fall, one of the very necessary things is to produce 
a mulch as early in the spring as possible with some implement 
adapted to that purpose. 

(e) Summer Tillage and Cultivation. — Alternate cropping 
provides for a crop every other year. To leave the land idle or 
occupied with weeds would be of no benetit. The object of not 
cropping during one season is to store moisture for the crop the 
following year. It is necessary then to put the soil in condition not 
only to absorb the rain that may fall, but to conserve it afterward. 
If weeds are allowed to grow the moisture will be lost. To avoid 
this loss summer tillage or fallowing is practiced. This fits the 
soil for absorbing water, for conserving it from evaporation by a 
mulch ami kills weeds that use it. 

Cultivation of crops is as important as sunuuer tillage and 
should be done to a greater depth than in humid regions. It may 
be done without injury to the roots of the crops, because the root 
systems of plants develop deeper in arid than in humid soils. The 
mulch produced on the surface should not be too fine, but made up 
of small clods mixed with fine granular material. If a dust mulch 
is produced, the first dash of rain causes the soil particles to nm 
together and produces a somewhat impervious stratum which pre- 
vents rapid absorption and water is lost through surface run-off. 
Every effort must be made to maintain a mulch until a network 
of roots is developed and the crop is large enough to shade the 
ground. Another objection to the dust mulch is that the fine mate- 
rial is so easily moved by the wind that serious loss of soil may 
result. 

After a shower falls, the mulch should be renewed as soon as 
possible. Experiments have shown that of the water lost during 



DKY-LASl) ACJJ'JCCL'ICJli-: 



247 



the first week after a rain GO per cent occurred during the first 
three days, hrtDc-.a the Tic-oc-.ssity for cultivation as soon as possible. 

(d) Subsurface Packing. — Newly plowed soil contains many 
large air spaces and is too open for retaining water against evapora- 
tion. Subsurface packing is resorted to for closing these air spaces 
iiml j^reventing excessive loss of water by evaporation. This is 
accomplished in a variety of ways. Figure 107 shows the subsur- 
face packer which is used for this purpose. The wedge-like wheels, 
five inches apart, crowd the soil to both sides, thus compacting the 
subsurface, but leaving a rnulch on the surface. This implement 
was invented by Mr. II. W. Campbell, of Lincoln, Nebraska, one 
of the pioneers in dry farming. 

Other methods are resorted to for compacting the subsurface, 




mpbfcll Subsurface Packer. 



such as using the disk set straight. The ordinar}' smooth roller 
would not be desirable for this purpose, becau.se the compaction 
that it produces renews capillarity at the surface and would cause 
a loss of moisture unless a mulch were again produced on the sur- 
face. In fact, the .smooth roller should never be used on a dry farm, 
as the flat surface produced encourages the soil to hlow. The cor- 
rugated roller leaves the soil rough and this prevents or at least 
greatly lessens blowing. The rolling should not he done parallel 
to the direction of the prevailing winds, but at right angles to it. 

(e) Storing of Rainfall. — A very important factor in dry farm- 
ing is the storing of the rainfall of one year in the soil for the 
use of the crop the coming season. The major part of the zone 
in which the water is stored should he sufficiently deep so that it is 
beyond the depth of ready capillary movement to the surface and 



248 



SOIL PHYSICS AND MANAGEMENT 



within the limit of the root zone for phmts under arid conditions. 
This varies from eight to ten feet or more in depth. Experiments 
in Utah showed as much as 951/^ per cent of the water which fell 
as rain and snow during the winter was found stored in the first 
eight feet of soil in the spring. Atkinson found that at the Mon- 
tana Station soil which contained T.7 per cent of moisture in the 
fall contained 11.5 per cent in the spring and after proper summer 
tillage contained 11 per cent in the fall. The following tahle shows 
the amount of water that may be stored in the soil during the 
winter : 

Percentage of Water in Each Foot of Soil to a Depth of Eight Feel ^ 





First 


Second 


Third 


Fourth 


Fifth 


Sixth 


Seventh 


Eishth 


Aver- 




foot 


foot 


foot 


foot 


foot 


foot 


foot 


foot 


age 


Sept. S, 1902 


6.37 


7.32 


8.17 


8.55 


8.26 


9.29 


10.10 


10.38 


8.56 


April 24, 1903 


19.29 


19.08 


18.83 


16.99 


13.61 


12.62 


12.24 


12.37 


15.63 


Increase 


12.92 


11.76 


10.66 


8.44 


5.35 


3.33 


2.14 


1.99 


7.07 


Aug. 24, 1906 


8.33 


7.63 


8.42 


9.66 


11.30 


10.75 


9.59 


7.93 


9.20 


May 1, 1907 18.17 


16.73 


17.96 


16.88 


16.59 


16.25 


14.98 


13.48 


16.38 


Increase 9.84 9.10 9..34 7.22 5.29 5.50 5.39 


5.55 


7.18 



.- It will be noted that the increase of moisture amounted to eight 
inches for the eight feet of soil. Water storage in a soil is impos- 
sible when a crop of weeds is growing. 

System of Cropping. — There can be no continuous cropping 
in dry-land agriculture as in humid regions, because the rain- 
fall is not usually sutKcient to grow two crops in succession. 
However, if the rainfall of two seasons can be used for growing a 
single crop, profitable results may be obtained. The conservation 
of this moisture from one season to the next is the most important 
problem in this kind of agriculture. The possibilities of raising 
grain under dry farming methods are seen in figures 108, 109 
and 110. 

Continuous Cropping vs. After Fallow. Average Results for All Years Tested, 
Montana Station'' {Bushels Per Acre) 





Kubanka 
spring \rheat 


White huUess 
barley 


Sixty-day 

oats 


Sub-station 


Con- 
tinuous 


After 
fallow 


Con- 
tinuous 


After 
fallow 


Con- 
tinuous 


After 
fallow 


Dawson County 

Rosebud County 

Yellowstone County 

Chouteau County 


15.18 

16.98 

7.73 

14.18 


17.57 
20.80 
19.32 
17.35 


15.97 
15.02 
14.90 
13.29 


20.90 
28.31 
20.33 
11.95 


31.17 
30.31 
13.75 
28.90 


51.00 
40.03 
^47.94 
34.56 



«^ 




Fig. 108. — Turkey Red Fall Wheat, without irrigation, jdeld 58 bushels per acre. (Mon- 
tana Station, Bui. 74.) 
Fig. 109. — White Hulless Barley on land continuously cropped. 

Fig. 110. — White Hulless Barley on land fallowed the previous j'ear. (Bui 74, Montana 

Station.) 



250 



SOIL PHYSICS AND MANAGEMENT 



The results show that fallowing gives considerable increase over 
-continuous cropping. The longer this is continued the greater the 
difference. Whether alternating crops with summer tillage is 
profitable will be determined largely by local soil and climatic con- 
ditions that influence the cost of production. 



Summer Tillage With Alternate Cropping vs. Continuous Cropping,^ North 
Dakota Station {Bushels Per Acre) 



Station 


Treatment 


Wheat 


Oats 


Barley 


Corn* 


Edgeley 

Dickinson 

Williston 

Hettinger 


fContinuous 

1 Summer tillage .... 

^Continuous 

1 Summer tillage .... 

/Continuous 

1 Summer tillage .... 

f Continuous 

\Summer tillage 


13.2 
14.8 
15.6 
27.8 
14.2 
19.8 
11.2 
21.5 


26.8 
42.5 
30.8 
51.1 
29.5 
46.0 
34.8 
48.6 


17.0 
20.0 
25.5 
32.5 
16.1 
28.8 
23.7 
31.8 


3610 
3400 
3750 
2880 
6890 
7370 
5840 
5540 


Average increase for Summer tillage 


7.5 


16.6 


7.7 


-225 



*Pounds. 

' It will be seen from this table that summer tillage gave an 
increase for wheat, oats and barley, but best results were obtained 
for corn by continuous cropping. 

Crops for Dry Farming. — In no kind of agriculture is the 
adaptation of the crop to the environment of greater consequence 
than in dry farming. In general, the crops should be such that 
a maximum growth is secured with minimum water requirements, 
and the crops that meet this condition Tvdll be best adapted to 
dry-land agriculture! Alfalfa is an exception, but its deep-root- 
ing character has fitted it for securing a large amount of water. 
Most crops have the power of adapting themselves to some extent to 
the conditions of climate after a few years, but the dry-land farmer 
needs a variety of crops that have been tried and developed by 
selection so that they resist the unusual conditions to which they 
are subjected. Upon the selection of the crop and seed may depend 
the success or failure of his efforts. 

(a) Wheat is the principal crop for the dry-land farmer. All 
over the arid and semi-arid regions wheat has proved to be one of 
the best drouth-resistant crops that can be grown. In the dry-land 
regions of other continents wheat has been grown for many cen- 
turies, and certain varieties have been developed which are well 



DRY-LAND AGRICULTURE 251 

adapted to arid conditions. Both spring and winter wheats are 
grown, the latter being much more desirable where the climate is 
suitable. Spring wheats are grown largely from Nebraska north 
through the Dakotas because of the severe winters. Two varieties 
of spring wheat are grown, the common spring wheat and the 
Durum or Macaroni. The latter was introduced from Russia and 
has proved to be an excellent variety. The semi-hard winter wheats 
are grown over extensive areas, the most hardy varieties being 
Turkey Red, KZharkof and Crimean, all originating in semi-arid 
Russia. 

The yield of wheat on the dry farm is of a great deal of conse- 
quence because it is the chief money crop. Winter wheat yields 
better than spring wheat. It usually pays to grow either on summer 
tilled land. In the dry-farm experiments in Montana the average 
yield of Turkey Red was 37.7 bushels per acre, while the spring 
wheat, Kubanka, was 18.4 bushels, or about half as much. In 
Utah Turkey Red produced 28.1 bushels, while the best spring 
wheat for the same years produced 14.6 bushels per acre. 

(b) Oats are beginning to be recognized as a good dry-land 
crop, either for hay or grain. Of the spring varieties the Sixty Day 
has proved to be best, principally because it ripens two weeks earlier 
than other varieties. A winter variety, the B'oswell, that has been 
tried in Utah, promises well. In 1907 and 1908 Sixty Day oats 
yielded 42.3 bushels per acre, while the Boswell gave 40.1 bushels. 
At the Montana Station the yield of Sixty Day was 37.0 bushels. 

(c) Rye is one of the best dry-land grains. It resists drouth 
better than almost any other cereal. The fall rye at Montana 
yielded 28.5 bushels per acre. The most serious objection to it is 
its persistence in the field after once seeded. It may be used to 
good advantage as a green manure. 

(d) Barley is one of the cereals well adapted to dry-land if 
seeded very early in the spring so that it gets a good start before the 
dry, hot weather begins. The hulless varieties seem to do best. In 
Montana as an average of all tests on different fields the yield of 
the White Hulless was 17.8 bushels per acre, while the California 
yielded one bushel more. In North Dakota an average of 23.8' 
bushels was obtained. One winter variety has been grown. 

(e) Corn has not been grown very extensively on dry-land 
farms because it is not well adapted to the temperature condi- 
tions found in arid regions. Corn does best where the nights 
are warm, and in arid regions the radiation is so great as to lower 



2o2 



SOIL PHYSICS AND MANAGEMENT 



the tomperaiiiro vovv imkh during' the niii^ht. Corn has oom- 
paratively low waior roquironioni and produces more dry u\alter 
for the water used than almost any other erop. Several strains 
have been developed that resist drouth well. When aeelimated 
seed is used, seed bed properly prepared and the erop well culti- 
vated, a failure rarely ever oeeurs. lu almost every season suf- 
ficient fodder is produced to pay for tlie crop, and in the more 
favorable years good yields oi' grain are obtained. Its principal 
value lies in the forage it produces. Figure 1 1 1 shows corn grown 




Fig. 111. — Corn gt\nvii on ilry-hind I:irm. Note low stalks. Utah. 



on a dry-land farm. The stalks are not so coarse as in humid 
areas aud make better feed. 

(f) Spelt and Emmer have been recommended as crops well 
adapted to somi-arid conditions. They were imported from Eussia, 
where they have been grown quite extensively as feed for stock. 
They are very closely related to wheat, but the hull reuiains attached 
as with barley. 

(g:) Sorghum is one of the principal drouth-resistant crops and 
yields as much as seven tons per acre. Its chief use is for forage. 

[h) Kafir and Mile Maize. — These are well adapted to the 
Great Plains south of Xebraska and parts of California. The 
temperature of the higher altitudes is too low for its growth. These 



DRY-I.ANJ) AGRICUL'l'URE 



253 



arc used both for i'orfx^o and ^rjiiii. In IIk; soiiUidrn pjiri of the 
(jireat J'lains iji Kansas, Oklalioina, 'J'cxaH and New M.exi(;(j Lhesc 
form a very important crop. Jurdinc" states that tlic avera^t; yield 
of shclhid ^Tiiin from niilo jnaiz(; was U) Inislicls p(;r a(;rc in the 
Panhandle of Texas. 

Where a severe drouth oct-urs these crops stop <4rr)win^' Ijut re- 
main alivc!. '^rhcy start quickly a^ain when rains come. 

(i) Alfalfa. — Ko crop has heen of <:creater value on tlie irri- 
gated land of , the West than alfalfa, and it is proving to he a very 
vnln;il)le'crop on the dry-land rnrni as well. Tt is, however, very 
didicnit to start under firid conditions. The fact that the roots 
penel,rat(! to siif;h a great depth in these; dry-hind areas makes it 




Fi(i. 112. — Dry-fun. I iimLmI. 



adapted to using the moisture stored to a great depth in the suh- 
soil, and no single season's drouth will all'ect it seriously after it 
becomes thoroughly established in the soil. Thick seeding must 
be avoided. It is better adapted to light and medium soils than 
to heavy clays. Cultivation is as essential in growing alfalfa as for 
any other crop. The seed crop is one of the most profitable of the 
alfalfa field. For producing seed it is best to plant the alfalfa in 
hills or rows so that it may be cultivated. It may be necessary 
to thin it to one plant every six to twelve inches. The second crop 
is usually left for seed, the amount of seed produced varying from 
150 to 800 pounds j)er acre. 

(j) Potatoes (Fig. 112) are coming to be looked upon as one 
of the staple crops of dry-land agriculture. With a rainfall of 12 
inches or more potatoes produce excellent crops, both in yield and 



254 



SOIL PHYSICS AND MAXAGE:^IEXT 



quality. An average yield of l"^o bushels per aere was produced 
ou the Montana Experiment stations in the dry-farming areas. 

Seeding. — In semi-arid regions seeding must be done more 
carefully than in humid regions. A deep mellow seed bed must 
be thoroughly prepared and too much work cannot be expended 
upon it- The seed bed should be such as to act as a storage reser- 
voir for water and siifficiently compact so that the moisture will be 
near the surface to germinate the seed. After the seed is planted 
or during the process of planting the soil should be compacted 
aroimd the seed. For this reason the press drill should be used 
quite generally in seeding. It permits uniform distribution and 
coveriuij of seed. Broadcast seedinir invites failure. 



yjrtfc! of Lofthouse Wheat With Different Methods of Seeding, ^'> Utah Station 
{Busheh Per Acre) 



County 


Method of seeding 


1904 


1905 


1906 


1907 


190S 


Averajse 


Tooele. . . 

Juab. . . . 


Broadcast 

■i Drilled 

iCross drilled. . 

"Brov^idoast 

^ Drilled 

Cross drilled . . : 


12.5 
15.2 
13.5 

16.7 
24.5 
IS.O 


5.5 
13.5 
13.0 

13.9 
16.9 

S.5 


15.0 
16.4 
13.3 

25.6 
33.5 
24.4 


16.0 

19^9 

S.6 
37.6 
30.0 


15.3 
24.9 
19.2 

12.9 
33.4 
11.9 


12.9 
19.9 
15.9 

15.6 
29.2 

1S.6 



From the preceding table it will be seen that the drilled wheat 
g-ave an increase of T.O bushels in one case and 13. li bushels in 
another over the broadcasted. 

On semi-arid land it might be supposed that deep seeding would 
be necessary. The depth must depend upon the character of the 
soil and the amount of moisture it contains. In heay\' clay plant- 
ing should be from one to one and one-half inches, while planting 
in sandy loams may be as deep as three inches. TThere wheat was 
planted three inches deep in heavy clay the yield for an average 
of five years was 1S.3 bushels, while where the planting was done 
at one and one-half inches the yield was 26.9 bushels per acre.^^ 

The amount of seed to the acre should be a little more than half 
that required in humid regions. A heavy seeding results in almost 
c-ertain failure. It very freqtiently happens that the moisture in 
the soil will be sufficient to start the plants of a light seeding in 
fine shape, while those of a heavy seeding would all be stunted. 



DRY-LAND AGRICULTURE 



255 



The Colorado Station recommends the following amounts, al- 
though this may vary with the condition of the soil : 

Pouruh of Seed Per Acre for Different Crops '^ 



Crop 


Pounds 
per acre 


Crop 


Pounds 
per acre 


Wheat 


30 to 40 

35 to 50 

20 

45 

10 

25 

25 to 30 


Milo maize for grain. . . . 

Dwarf Essex rape 

Brorne grajss 

Alfalfa for hay 

Alfalfa fultivatedfor seed 
S\veet clover 


5 to 8 


Barley 


3 to 5 


Flax.... 


20 


Spelt and emmer 

Millet 


12 to 20 
2 to 3 


Sorghum for forage 

Kafir corn for forage 


20 to 25 



Com, single grain.s, 15 to 18 inches apart. 

Merrill of Utah recommends that oats and barley be seeded at 
the rate of three pecks per acre; rye, two pecks; alfalfa, six pounds, 
and other crops in proportion. 

Acclimated Seed. — The seed to be planted on a dry-land 
farm should ha\e been grown under semi-arid conditions. 
Farmers from humid regions frequently take seed with them when 
they go on the dry farm and crop failure results. Usually several 
years are required for a crop from humid regions to become 
thoroughly adapted to its new conditions so that it will produce well. 
It is far better for the farmer to obtain seed already accustomed 
to dry conditions. 

QUESTIONS 

1. Upon Avhat three things does the adaptation of land for dry farming 

depend ? 

2. What conditions of soil are best? ^Vhat are objectionable? 

3. From the standpoint of water requirements, what are some of the good 

crops for dry farming? 

4. How does cultivation lessen the Avater requirement of crops? 

5. Why do crops on summer fallow produce more than where cropped con- 

tinuously ? 
('). What conditions in arid regions make a large run-off possible? 

7. What conditions allow a large evaporation? 

8. What is the most desirable depth to plow in drv farming? 

0. Why is fall plowing more desirable under dri'-farm conditions? 

10. Give the advantages in the use of the subsurface packer. 

11. To what extent may the fall and winter rain and snowfall be stored 

in the soil for crops ? 

12. What about weeds on a dry-land farm? 

13. How does transpiration vary? 

14. What important points should be obserA'ed in selecting crops and seed 

for the drv farm ? 



256. SOIL PHYSICS AND MANAGEMENT 

15. Give the advantages of wheat for the dry-huul farm. 

16. Wliy is a fall or winter variety more desirable than a spring-sown one? 

17. What special advantages has corn for semi-arid regions? 

IS. Why is alfalfa a good dry-land crop? How is a seed crop produced? 
is'. A\hat precautions must be taken in seeding the crop in dry-land 

farming ? 
1^0. What is meant by acclimated seed? Why is it imi)ortant? 

REFERENCES 

MVidtsoe, J. A., Dry Farming, U)ll, p. 132. 

^ Brigiis, L. J., and Shantz. H. L.. Journal of Aiiricultural Research, vol. 

ill, No. 1, ISlll. pp. 5S-U0. 
'Widtsoe, J. A., Drv Farming, IDll, p. 185. Principles of Irrigation Prac- 

tice, 1914, p. 141. 
■• Rotmistrov, V. G., Nature of Drought, English edition, 1913. 
^Merrill. L. A., A Report ot Seven Years' Investigation of Drv Farming 

Methods, 1910, p. 133. 
MYidtsoe, J. A., Drv Farming, 1911, p. 114. 

'Atkinson, A., and Nelson, J."p., Bulletin 74, :Montana Station, 1908, p. 83. 
^Thysell, J. C, and others, Bulletin 110, North Dakota Station, 1-915, 

*pp. 183-18.1. 
^Jardine, W. M., Circular 12, Bureau of Plant Industry, U. S. D- A.„ Dry- 

Land Grains, 1908, p. 0. 
"Merrill, L. A., Bulletin 112, Utah Station, A Report of- Seven Year^' Inves- 
tigation of Drv Farming INlethods, 1910, p. 139. 
"Op. Cit., p. 138. 
^ Cottrell, H. ]M., P.uUetin H-'i. Colorado Station, Dry-Land Farming in 

Eastern Colorado, 1910, p. 23. 

General References. — Olin, W. H., Bulletin 103, Colorado Station, 
The Thorouiili Tillaye Svstem for the Plains of Colorado, 1905. Failver, 
G. H., Farmers' Bulletin 200. U. S. D. A., 1900. Jardine, W. M., Bulletin 
100, Utah Station, Arid Farming Investigations, 1900. Scofield, C. S., 
Bulletin 103, Bureau of Plant Industrv, Drv Farming in the Great Basin, 
1907. Campbell, H. W.. Soil Culture Manual. 1907, Lincoln, Neb. Nelson, 
Elias, Bulletin 02. Idaho Station, Dry Farming in Idaho, 1908. Burr, 
W. W., Bulletin 114, Nebraska Station, Storing Moisture in the Soil, 1910. 



CHAPTEE XXI 

CONTROL OF MOISTURE 
IV. IRRIGATION 

Ieeigation may be practiced in any region where the normal 
rainfall is not sufficient to grow maximum crops or where the 
rainfall is deficient during any |)art of the season. The profit 
realized will depend upon the crop grown^ the increase in yield over 
no irrigation, the cost of applying water, and the j)rice of the crop. 
The practice is usuall}^ confined to arid regions because irrigation is 
absolutely necessary under those conditions to -produce any -crop 
whatever, or to semi-arid regions where' irrigation wifltgive larger 
3'ields and in some very dry years would insure a crop V^ere other- 
wise there would be none. Irrigation is practiced to a v^ry limited 
extent in humid climates, even in Florida with from fifty to sixty 
inches of rainfall and in other states" with thirt}^ to torty; inches. , 
In these regions water is applied in a very intensive form of agri- 
culture or to special crops which command a high price, thus jus- 
tifying the expense. In some European countries sewage is some- 
times applied to soils, thus furnishing both water and plant food. 
In China and Japan irrigation is an almost universal practice, even 
where much of the land receives a fair natural supply of water in a 
Avell distributed rainfall. 



Some Irrigation Projects in Western United States 



Salt River, Arizona 

Yuma, Arizona-California 

Uncompahgre, Colorado 

Boise, Idaho 

Minidoka, Idaho 

Flathead, Montana 

Milk River, Montana 

Sun River, Montana 

North Platte, Nebraska-Wyoming 
Shoshone, Wyoming 

17 



Approximate 


Acres to be 


cost 


irrigated 


$10,000,000 


219.000 


7,000,000 


130,000 


5,000,000 


140.000 


8,700,000 


243,000 


4,400,000 


118,000 


1,2.-0,000 


152,000 


1,060.000 


219,000 


1,000.000 


216,000 


16,200,000 


129,000 


3,800.000 


164.000 



257 



2oS 



SOIL PHYSICS AND MANAGEMENT 



The axea of laud that may ultimately be brought under irriga- 
tion is small in LX)mparison Trith the t^tal dry-land area, because 
the total supply of ^ater is not sufficient for more than one-tenth 
of the dry land. At present only about one per cent of the land in 
the western states is irrigated. The building of such reservoirs 
as are given in the prec-eding table is extending the irrigated area 
more than was supposed to be piossible a few years ago. 

Area and Projects. — In 1909, 13.:39.499 acres of land were 
irrigated in the arid states. This was an increase of S"2 per cent in 
ten years. In 1910 the projects, then started, will be capable of 
irrigating 19.335,711 acres when fully under way. The total area 
included in the projects is 31,112,110 acres. In addition to tbe 




Fig. 113. Fig. 114. 

FiQ. 113. — Conduit for conducting water to where it maybe used for irrigation. (U. S. 

Reclamation Service.) 
Fig. 114. — Concrete-lined canal that permits no loss by seepage. ^t". S. Reclamation 

Sexvice.l 



above, T 24,800 acres of land were irrigated in humid areas, nearly 
all of which was for the growing of rice. 

The United States Eeclamation Service, established in 1903, 
was to use the money from the sale of public lands in the arid states 
in the c-onstruction of irrigation systems. Under the direction of 
Dr. F. H. Xewell immense projects have been started, many of 
which have been completed, and by which large areas have been 
reclaimed and added to the country as some of its most valuable 
assets. 

Sources of Water. — (a") Diversion of Streams. — ^The com- 
mon sourc-e of water for irrigation has been the diversion of parts 
of streams at a height above where it is to be used and c-onducting 
it by means of canals, tunnels, conduits and ditches to where 
it is to be distributed over the land (Figs. 113 and 114). 



IRRIGATION 259 

Water is sometimes conducted for many miles, passing through 
hills and over valleys and gorges. In the case of the Gunnison 
tunnel of Colorado, the Gunnison river is diverted from its course 
and carried through a tunnel almost six miles long, pouring into 
the Uncompahgre Yalley, where it is used to irrigate 140,000 acres. 

(b) Reservoirs. — In many places in the arid regions of this 
and other countries dams have been built across gorges or narrow 
valleys, producing lakes or reservoirs whose water is used in the 
irrigation of tillable land farther down the valley. In this way 
the rains and snows of winter, which would otherwise be lost, are 
held for the use of crops at a time when the water of the stream 
is entirely insufficient for the purpose. The Eoosevelt dam across 
the Salt Eiver in Arizona is a good illustration (Fig. 115). Here 
sufficient water is stored for irrigating 219,000 acres. This dam, 
curved upstream, is 281 feet high and 910 feet long, with a thick- 
ness at its base of 168 feet and 20 feet at the top. It forms a lake 
or reservoir 25 miles long and from one to two miles wide and con- 
tains 1,367,000 acre-feet of water. Many similar systems have been 
constructed by the government, or are under way, that "n-ill irrigate 
from 10,000 to 225.000 acres each, making a total of over 3,000,"000 
acres irrigated by these projects (Fig. 116 ) . 

(c) Pumping from Some Subterranean Supply. — In some 
localities in arid regions extensive underground reservoirs of water 
occur sufficiently near the surface to be pumped for irrigation pur- 
poses. In other regions artesian wells may furnish a bountiful 
supply. Where irrigation is practiced in humid regions pumping is 
the usual method. The rice fields of Arkansas and Louisiana are 
irrigated in this way. 

(d) Pumping from Streams or Canals. — In Egv-pt, India, 
China and Japan much of the water for irrigation is pumped on the 
land by means of hand or foot power. Sometimes cattle or donkeys 
are used for this purpose. 

Preparation of the Land for Irrigation. — The first step in 
preparing the land for irrigation is the removal of the vegetation 
(Fig. 117). The character of this varies with the amount of rain- 
fall from stunted grass, sage brush, greasewood, and niesquite to 
the remains of hea^y forests. The cost of clearing varies from two to 
five dollars per acre for most lands to as much as one hundred and 
fifty dollars per acre for forests. After the vegetation is removed 
the land must be graded so that the water mav be uniformly ap- 
plied. Man}' tracts are so flat that very little grading is necessary. 



200 sou. rUYSlOS ANP MANAOKMKN r 





Fro, H5, — Eo<*s>?v«'h Dsiiv. Sssli Riwr, Ansv>ns»> >.ir, ?, Rcfclsunatioa Service.'* 
Fm. I lit*. — 0;r*:ii?e Ktx-i Diwrsioa Dswa: Sah Riv*r Prv\)<f<ft, Ariioaa. vU, S, Kf 



IRRIGATION 



261 



Usually there are depressions to be filled or slight elevations to 
be removed. The object is not to level the land, but to reduce 



Fig. 117. 



'-mr.M'^^^M. 



^ 



iSfe 



"^•^■•lA^ *---' 








Fig. 11& 
Fig. 117. — Desert lands and Homestead, Huntlej' Project, Montana. CU. S. Reclamation 

Service.) 
Fig. lis. — Wheat field, Minidoka Project, Idaho. Yield 60 bushels per acre. '^U. .S. 

Reclamation .Service.) 

it to a uniform slope so that water will spread over it uniformly. 
(Fig. 118). 

Character of Water Used for Irrigation. — In humid regions 



262 SOIL rUYSlC^ AND MANAGEMEXT 

the wsror o: si^sjins oarne* but iitrle SvUuble maierial, but iu arid 
suui seiuisiTid r^ioais, whero the gry?at nec^sssity for irrigaticoi 
eii$t$s both $oil and w^ter may .xaitaiu alkali in considerable abun- 
dance. While the e:xee!5s: of alkali in irrigated lands is due usually 
tv> The salts in the soil, yet it is in many eas*s? due in part, and some- 
timets vhoUy, to the salinity of the water which is Knng nsevl for 
irrigatiiMi. The salrs thus carried accumulate in the soil, pKv- 
ducing \«^y injurious n>sults- Forty grains of salts per gallon is 
usually assigned as the limit for irrigation xraters. This, however, 
depends upon the character of the substances in solution. In Call- 
fisrnia the limit lies in all osises below TO grains. The danger of 
using irrigation water twniaining considerable salts depends very 
largely npoai the drainage of the land irrigatevi or the methods of 
pi^Tienting their accximulation. 



;^^jhihM .VoOtT M JStm- ITafoTS ^ 




BiT«r 


P»^pef bSKmi 




XBaiaai^si MaxxBMtm 



Bdife fburdK', xt BeBe Fourdke, Soutk Dsakota . 

Bt^bora. at Fort O^ler, Montaon 

OMonfdOk at YumaL Aniona 

BedL at Maxmm. OidakoiBa 

firninrrin at wTutewawr. Coktrstdo 

Be««s. 31 Cciirfebad. New Mexko 

Pwv"^ St r>s>-TCGi. Xevr Mexieo 

Rio i>s3ie, ST Fi Psscv. Texas 

^ih. at Rixe^T-eh, Araosa 



56 


7.130 


IS 


iseo 


741 


sasai 





ld.S0O 


32 


4.0» 





1.4S0 


-J4 


11.44.X> 


N 


SS.900 


40 


d.1*iD 


^ 


Iv4-?0 







orks? r >-; i: ;;:5v iision wh:_: ::: ? :. : ::ur:r:^r^: ;^:: :r 
in i»£ J the fertiliiT of the soil- The amount of sediment 

oarie^ ^ ^.T^ttaon by wkvs ^leams fe gi^en in tibe aboTe 

Cc" - ? : - - : River Sediments. — ^Many river sedimeiits have 

heen ii . . - .;; Vi:::ed Stsres, in Etii>oj^, and in Egypt. The 

resahs show ihai river muds aii? somewhat iwd«r in the essential 
plant ' ' ~ ~ -V fertile seals from wfaidi tlie 

water - \ ^v Forbes that the mai^t 

rafale : : r^ee 5amT>le? of Sah Biver 

HMd,: #7.9? to 1^-5-51-= Whea 

Ijbe fcr ~ - - ^ considered in eomeeiiQa 



IRRIGATION 263 

with the value of the dissolved materials, one of the great advantages 
of irrigation is made evident. By this addition of plant food from 
year to year cropping may continue indefinitely without depleting 
the soil. Some streams are exceptions to this rule, however. 

Time of Irrigation. — The irrigation of crops may take place at 
various times, depending upon the crop grovra and the object to 
be accomplished. Theoretically the soil should 'be supplied with . 
just sufficient water to maintain optimum conditions for growth 
and maturity. This is a condition to be desired, whether ever at- 
tained or not; however, this is rarely possible, since the supply of 
water frequently runs so low that during part of the growing 
season it is not adequate for the purpose. 

Irrigation may be done either when the crop is not growing, in 
the fall, winter or early spring, or when the crop is growing during 
the summer. In the former case the object is to obtain the water 
when the demand for it is not so great and store it in the soil for 
use the next season. It may be done immediately after harvest and 
from then till spring. Winter irrigation is not advisable when the 
soil is frozen, as much of the water may be lost, but where the win- 
ters are mild it- may be practiced to good advantage. 

Alfalfa and wheat should not be flooded during the winter in 
cold climates. 

Irrigation water may be applied early in the spring to save some 
of the water of the spring floods caused by the melting snows of 
the mountains. This would be largely lost unless reservoir have 
been built to store it for summer use. The time and frequency of 
irrigation depend upon the crop. In Arizona orchards receiving 
fall and winter irrigations have produced well without any further 
application of water. Alfalfa should be irrigated several times, a 
few days before cutting and again soon after the crop has been 
harvested. Wheat and other small grains, beans and peas if planted 
in a soil well filled with moisture need little or no irrigation till 
flowering time. This permits a good root system to develop. Early 
irrigation lessens the proportion of grain to straw. 

Amount of Water to Apply. — ^As a general rule the more 
water that is applied to a soil, within practical limits, the larger 
amount of dry matter it produces. The problem is not to go beyond 
the point of most profitable returns. This point has not yet been 
determined. It is Terr difficult of determination, since it varies 
with the crop, the soil, rainfall and other conditions. 

Usually more water is applied than is necessary and certainly 



564 



SOIL FHYSICS AXD MA^^\Gi:MEXT 



^"'S Z3E 



!-~ X — -^ • ■ 

— — . ^> . - 



t^ cs X ic 



~ ' _; ^5 r^ 
S I — t" 



F2 '~ t^ 'T-" -w- "* 



~t X* 2! ^ ~. S ^' T 






"^ — ^O '^»rtX '^CiX tCT:^"r*X r>»03t^ ,c 



^-• '^ £2 li 









- 1: O X 3: _- i r< — 
— X i — r» 





,_ ^ ^ — 






— C^ 




r^ ^ -r n 


.^ 


t"^ ■*"■ TZ *-^ 






*^ *C re — 




■^ re ^ .i- 


^ 


£2 o ^ r 






tr — "^ r; 




— ri "' 




























^ -^' ^ ... 


-* 


— :=X 




tcc::^ X 


t^=: t>»^ 


_ 


>. — ~ X 


:^' 


X — ri 




r-5 X — r^ 




=. 




^ 


t^ "^ *~ 




— ' o ^^ ^ 


-*r CC ^r ^~ 


^ 


— "^ rt 




-^ — if 




~- — — i: 


^ r*^ 






J j: ? is 



s ^. = 5^ 5 I - = i I - 1. i ^ - 5 ^;^ = i ^^^ 1. 



>^ 






'Z < X — 



IRRIGATION 



265 



more than is econoinieaL In the table the additional amonnts of 
water appKed gave aa increase in the total drr matter prodneed, 
yet the increase of dry matter per acre-inch of water decreased- 
The increase obtained was not always profitable. It wilL be noted" 
that the yield of wheat is 37.8 bnshels per acre wliere five inches 
of water were applied, while 7.5 inches gave a yield of 41..5 bnshels, 
or an increase of 1.5 bnshels per acre-inch. When 2.5 inches more 
were added the increase was 0.8 bnshel per ac-re-inch, and when fire 
inches more were appKed the increase was ()A bnshel per acre-inch. 
The next ten inch^ gave le^ than one-tenth of a bnshel increase 
per acre-inch. It i= very evident that the point of profitable appli- 
cation of water has been passed. 

The Proditcing Power of 30 Acre-Inchs^ TT^en Aj/jjfied io Di^ererii Areas 

of Land ^ 



30 Acie-iedbes epieaii crrer 





'^ne aere 


T-B-o ac-res 


Tsaee aerss 


l''jHir&iET=S 


SEaeiES 


C-p 


SO lac-fies 


io iii-ifjes 


10 merigs 


- .o iri-n«^ 


5 irif bes: 




-ee-p 


ce^p 


~^-e- 


-**i? 


"«P 


Wheat: 












Grai-. h-'-? 


47.51 


91.42 


1.30..59 


166.16 


22&.86 


."itra-s-. poTjifis 


... 4533 


7908 


1(»56 


13304 


17916 


Com: 








! 




Grain, bnshels 


97.12 


187.86 


268-56' 


1 316..56 




Stovw, pounds 


... ia390 


16a5S 


i^:'2i 


^756 




Tnnotiiy: 












Hav, pouiM^ 


. . . oasi 


.05.5 


117b'9 


11525 




Sogar b^ts: 












Tons 


20. S2 


3^.t^j 


a5.S& 


Oi-Si 


82.68 


Bnshi^s 


. . . 195 


373 


456 


i .544 * 


691 


.\Kah'a: 






i 1 






Hay. fKjTxnds 


- . SS40 


15093 


26653' 


i 





The one object to be kept in mind in irrigation is to grow the 
maximnm amount of dry matter with an acre-inch of water. Ex- 
periments show that 10 to 20 inches is the most practicable amonnt 
to apply. Larger amonnts lower tbe quality of the grain and do not 
give proportionate increases. 

The above table shows the valne of smali appKcations over more 
extensive areas in comparison to the s^ne applicaT:::! ■'.— smaller 
areas. 



266 



SOIL PHYSICS A^'D MANAGEMENT 



Returns from Sugar Beets Where SO Acre-Inches are Distributed Over Different 

Areas ^ 



Inches of Yield of Total 

1 _,.__ water on beets per yield of 
spreaa o\ er each acre acre- (tons) beets (tons) ■ 



30 acre-inches 



1 acre . . 

2 acres . 

3 acres. 

4 acres . 



30.0 
15.0 
10.0 

. .5 



21.0 
19.5 
18.6 

16.3 



21 
39 
56 

65 



Price 


Gross 


Total 


1 Net 


per ton 


returns 


cost 


' returns 


$5 


SlOo 


S 60 


$ 45 


o 


195 


120 


75 


o 


280 


180 


100 


5 


325 


240 


85 



From the above table it will be seen that 30 acre-inches spread 
over three acres gives the greatest net returns. The results of the 
Utah Station indicate that where the annual rainfall is 12 to 15 
inches an application of 10 to 20 inches is sufficient for ordinary 
cropSj and the best amount lies near the lesser quantity. Dr. F. H. 
Xewell is of the opinion that 12 acre-inches is sufficient to produce 
good crops of all kinds except alfalfa and a few other similar crops. 

Loss of Water from Canals. — It is everywhere agreed that a 
very large part of the water diverted from streams is lost before it 
reaches the place where it is to be applied to the land. It is esti- 
mated that 5. 77 per cent of the water is lost for each mile of canal 
through which it is carried. This means that all the water would 
be lost in 17 miles. The loss is caused by evaporation and seepage. 
The canals pass over all kinds of soil, both porous and impervious. 
Large amounts are lost where the canal passes over gravelly or 
sandy soil. This seepage water not only does very little good, but 
in many cases does much harm by causing the water table to rise 
injuriously near the surface and aLso brings up the alkali. Some 
expedients are used to diminish this loss. The soil is sometimes 
puddled by dragging chains in the bottom of the canals (Fig. 119), 
thus rendering the soil less pervious. The bottom and sides of 
canals are sometimes covered with crude oil to lessen leakage. The 
large canals are sometimes lined with concrete (Fig. 114), which 
limits the Ic^s to the evaporation. Even fine soil constituents, such 
as clay or silt, have been used for lining the canals to render them 
less pervious. This is accomplished in part by the sediment carried 
by water. 

It is estimated that in India the loss is from 20 to 75 per cent 
from the canals. The investigations of the Department of Agri- 
culture in this country show that nearly 60 per cent of the water is 
lost between the head gates and the laterals and a considerable por- 
tion of the remaining 40 per cent is lost before it reaches the land 



IRRIGATIOX 267 

to be irrigated- Fortier says that l^s t h R n one-third of the water 
diverred from the streams is actuallT iised by the crops. 

The Duty of Water. — '' The duty of water/' a term long since 
coined, means. the quantitT of water needed to mature crops. It 
mar be expressed in various ways. Sometimes the duty of water 
is expressed as the number of pounds of water required to produce 
one poTtnd of the dry matter of the crop; under otibier conditions, 
as the depth of water over the neld required during the growing 
season to produce the crop. 

•More commonly, however, the duty of water is expressed as the 
number of acres that may be irrigated by a definite quantity of 
water, say a second-foot, flowing continuously through the growing 
season. * A sec-ond-foot of water means that a cubic foot of water is 




delivered each second and may oe easily reduced to acre-feet or acre- 
inches, sicic-e at this rate an acre-inch will be delivered each hour. 

The absolute duty of water is the total amount that the crop 
rec-eives by irrigation, by rainfall, and that contained in the soil. 
It is expressed as acre-inches. The net duty of water is the amount 
actually delivered to the farmer through his head-gate. 

One second-foot serves to irrigate from 2-5 to over 300 acres 
during the growing season. An average is from To to 100 acres. If 
the acreage irrigated by a second-foot is small, the duty of water is 
low. while if the acreage is large the duty is high. 

The duty of water varies with several factors : (l) The rainfall 
varies in irrigated regions from almost nothing to 30 or 40 inehes. 
The acreage irrigated by a second-foot will necessarilv vary with 
the rainfall. (2) Soils that are quite porous will reauire more 
water for the crop than the less pervious ones, sinc^ much will 
be lost by percolation. Even hardpan soils require more water than 



26S 



SOIL PHYSICS AND MAXAGEMEXT 



those of uniform texture. (3) Dilfereut crops require different 
amounts of water. Forage crops, especially alfalfa, require more 
water than cereals. (4) A fertile soil requires less water than a 
run-down soil. (.5) The amount of water required depends to some 
extent upon the amount of water applied and the means taken to 
c-onserve it. 

Duty of Water in Different Countries. — Irrigation is prac- 
ticed on all continents. The duty of water in Eg}-pt is 115 acres 
for cotton and other dry crops and 60 acres for rice. This is for an 
irrigation period of 75 days. In southern Africa, where the annual 




Fig. 120. — ^Rectangular weir. 



rainfall is from 30 to 35 inches, the duty of water is, for vegetables 
100 to 180 acres : for cereals 140 to 200 acres ; for sugar cane 50 to 
75 acres. In India the duty from June to October is 80 to 170 
acres, while from Xovember to March it is 90 to 200 acres. Under 
some canals 160 acres have been adopted as the normal duty. 

In Europe the duty is somewhat higher than in most countries, 
because of higher rainfall. The average for Spain is 172 acres, 
while that for Trance, Spain and Italy is 239 acres. Investigations 
in Xorth America show that the duty of water is about 100 acres 
for an irrisration season of 90 days. 

Measurement and Distribution of Water. — Since water is a 
thing of such great value in irrigation, its measurement becomes a 



IRRIGATIOX 269 

necessity to protect the fanner xvlio is the purchaser or consmner 
and the company that furnishes the water. Many devices have been 
used, but the most common and most satisfactory is the weir or 
overfall (Fig. 120). The Tveir should be instaUed" where the canal 
is long, straight and level. A box is placed in the canal so that aU 
water must flow through it. A board with a notch is placed in the 
box and across the stream. This notch may be several inches or even 




Fig. 121.— Trapezoidal or Cippoletti weir, shoiring method of diTiding the ^ream Utah 
Agnculniral Expeiimeiit Station.) 

several feet long and the depth of water flowing through this mav 
be easily measured and the total amount determined from a table. 
These notches may be either rectangular, trapezoidal, or triangular. 
The trapezoidal is c-oming into most general use. 

For purposes of distribution to different laterals the streams 
are frequently divided at the overfall by placing a board with a 
sharp edge so as to separate the stream into two or more parts (Fi^. 
121). Each part is then conducted off in a separate lateral to the 
resrion desired. 



270 



SOIL ruYsics AND .manac,e:ment 



Methods of Irrigation. — The luanuer of applying wator to 
soils dororiuiuos to a largo extent the intlueiiee it has both upou 
the plant and soil as well as the etleeiiveness of the water itself. 

In arid regions two general systems of irrigation are followed, 
flooding ajul furrowing, eaeh of whieh has its advantages nnder 
otn-tain eonditions. The determining faetors are (1) the eharaeter 
of the soil, i^',?') the amount of water per unit of time or •"head," 
(o) the contour or lay of the land, and (4) the kind of orop. 

(a> Flooding. — A common method for applying water is by 







^•^IT'^ 




Fig. 122. — Basin or check s^-^tera of irrigiitiiis i^rvh:»i\i*. IMnoiples of 1? :-,ouoe, 

Widtsoe. ^Courtesy Maciuillau Company-.) 

flooding the entire area. This requires that the land shall be prac- 
tically flat and the soil one that does not erode badly nor bake 
upon drying. Heavy soils are best adapted to this method, so that 
when the large volume of water is turned on the soil will not wash. 
If the volume of water is tiX> small it will sink into the soil before it 
readies the other side of the field. Alfalfa, pastuiv and n^ieadow 
land and wheat and other small grains may be successfully irrigated 
in this way. Tliree principal modifications of this method are 
flootling closed tields. flooding oik'u fields and basin fiiXHling. The 
c^osed-feJd flooding or cheek flooding, as it is sometimes called, is 



IRRIGATION 



271 



where a levee or dike is built around tlic field and into wliicli tiie 
water is turned and left till it is all absorbed. 'J'his is a common 
practice in China aJid Japan. In open field flooding a canvas dam 
is placed in tlie ditch and the water forced to run over the banks 
of the ditch into the field. A moderate slope permits it to run 
slowly over the field where the surplus water runs into another 
ditch at the lower side. 

Basin flooding is practiced in orchards, the levee being thrown 
up so as to occupy the space allotted to each tree. The water is al- 
lowed to enter the enclosure and left till, it is absorbed (Fig. 122). 
Dirt is piled around the base of the tree so the bark will not get 
wet. This method is gradually passing out of use. 




Fig. 123. — Irrigating potatoes by furrows. U. S. Reclamation Service. 

(b) Furrow Irrigation. — The furrow method of irrigation is 
one of the most common and for most conditions one of the best 
methods practiced. Small furrows lead from the supply ditch and 
the water is absorbed by the soil (Fig. 123). The furrows are from, 
five to ten inches deep and from three to eight feet apart, the dis- 
tance depending upon the soil and the crop. By this method the 
ixrigator may control the quantity of water and a comparatively 
small amount may be spread over a large area of land. Only a 
small amount of the soil becomes wet, so that injury from puddling 
is not imminent. The furrows may soon be covered and thus reduce 
evaporation, preventing or retarding the rise of alkali. It is very 
difficult to obtain uniform distribution, due to the difference in the 
absorbing power of the soil or length of furrow or both. This 



272 



SOIL PHYSICS AND MANAGEIMENT 



method is specially adapted to iuter-tilled crops, such as corn and 
potatoes, and is used extensively for cereals, alfalfa, and orchards. 

(c) Sub-Irrigation, — The method of sub-irrigation is prac- 
ticed only to a very limited extent because of the great initial cost 
making it almost prohibitive. Iron, concrete or wooden pipes may 
be used, but digging the trenches for placing these is expensive. 
The roots clog the openings and in time impair the usefulness of 
the system. 

A form of natural sub-irrigation is practiced in the West where 




Fig. 124. — Method of irrigating by overhead sprays. Adapted to small fruits and 
vegetables in humid areas. (Fortier's Use of Water in Irrieation.y (Courtesy McGraw- 
Hill Book Company.) 



the soil is sufficiently porous so that no underground pipes are 
necessary. Former irrigation has brought the water table near 
the surface, and now the object to be accomplished is to keep the 
water table sufficiently near the surface so that capillary water from 
it will supply the crops. An impervious stratum is necessary at a 
depth of a few feet. A tract of 60.000 acres is irrigated in this way in 
the upper Snake Eiver Yalley, Idaho. Parts of the San Luis Yalley, 
Colorado, are irrigated in the same manner. The ditches are from 
50 to 250 feet apart. 

(d) Surface Sprinkling and Overhead Sprays. — This method 
is adapted only to small areas and is one of the most expensive as 



IRRIGATION 273 

well as ineffective ways of ajaplying water. It is distributed under 
pressure through pipes, the water escaping by means of nozzles or 
by small openings. It is used principally to supplement the rain- 
fall (Fig. 124) in humid regions where crops of high value, such 
as vegetables and small fruits, are grown. Usually the application 
is sufficient to penetrate only to a slight depth, hence it soon evapo- 
rates. It has a tendenc}' to produce shallow rooting of the plants. 
The method has the advantage of easy control, little waste land, 
and ma}^ be used on very uneven land. 

Cultivation After Irrigation, — Where possible the irrigated 
land should be cultivated as soon as the soil is in proper condition. 
The loss by evaporation following irrigation is enormous, especially 
where no crop is on the land large enough to shade it. The Utah 
Station found that where land was not cultivated till seven days 
after irrigation the loss of water by evaporation was 1.45 inches or 
164 tons per acre, while 14 days gave a loss of 1.93 inches or 219 
tons per acre, and 21 days gave a loss of 2.7 inches or 307 tons. The 
cultivation should be as deep as possible under the circumstances. 
As the result of an experiment a loss of 1.75 inches occurred in 
28 days where there was no mulch. When a layer of dry granular 
soil three inches thick was placed upon the surface the evaporation 
was reduced to 0.78 of an inch or 57.7 per cent, while a ten-inch 
mulch practically stopped evaporation. 

Crops for Irrigated Lands. — Practically all crops adapted to 
the climate will grow under irrigation. Some require more water 
than others, but this is easily adjusted by the applications of water. 
(Fig. 125.) 

Cereals. — Wheat. — The best cereal under irrigation is wheat. 
While it is primarily a croj) for dry-land agriculture, yet it yields 
well when irrigated and is a good crop to fit in with rotations used 
on irrigated lands, and is grown quite extensively. The amount of 
water required by wheat depends upon the perviousness of the soil, 
but in a deep, fertile, well-tilled soil 12 inches will be sufficient. 
The Utah Station found that an application of 7.5 inches of water 
gave 41.5 bushels, 10 inches gave 43.5 bushels, and 15 inches gave 
45.7 bushels per acre. 

Oats. — The growing of oats on irrigated land probably will 
never become very extensive, although it will be used to some extent 
to give variety in rotations. It produces well and requires about the 
same amount of water as wheat. 

Barley. — The barley crop is a valuable one under irrigation, 
18 



274 



SOIL PHYSICS AND MANAGEMENT 



produeiug well aud requiring a less amouut of warer than other 
cereals. After an applieation of 7.5 inches of water little increase 
was obtained with more. The barley produced under irrigation is 
of better quality than that produced on dry land. 



Fig. 125. 





i^t?:?^-. 



Fig. 126. 
Fig. 125. — Mallin Ranch, Salt River Project, Arizona. \U. 
Fig. 126. — Alfalfa field. Yuma Project, Arizona. J 



, Reclamation 
SerWce 



Corn produces more dry matter in proportion to the water 
applied than almost any other crop. It is not yet grown exten- 
sively under irrigation, but its area is increasing, especially in 
regions where stock raising is a prominent industry. It has a 



IRRIGATION 275 

longer irrigatioL period than snial] grains, therefore requires more 
water. Cultivation after each irrigation is very essential. An appli- 
cation of 25 inches gave 99.1 bushels per acre at the Utah Station. 

Bice is a crop that is groviii under humid, semi-tropical con- 
ditions, but irrigation or flooding is necessary. The check system is 
used. Le\'ees are thrown up sufficiently high to retain a layer of 
water to a depth of three to ten inches. The water is nearly always 
applied by pumping from wells or canals. 

Forage Crops. — Alfalfa is not only the mo.st important crop for 
forage purposes, but it is the most valuable of all crops grown 
under irrigation (Fig. 126). Its value is enhanced by the fact that 
it is a nitrogen gatherer and. actually builds up the soil during its 
growth. 

AVater may be applied by furrows, flooding, or by checking. 
When water is abundant flooding is the method used. If the soil 
Ijakes or tends to run together, the furrow method is preferable. In 
this case the land is marked off or furrowed immediately after seed- 
ing and the furrows become permanent. Alfalfa requires somewhat 
more water than cereals, and 18 to 24 inches should be applied. 
Fortier found that 30 acre-inches applied to one acre produced 
14,400 pounds of hay, while when the same amount of water was 
applied to five acres 04,100 pounds were produced. 

If seed is to be produced but little water should be applied to 
the growth that is to produce the seed. 

Other Forage Crops. — Timothy, orchard, grass and hrome grass 
are crops that thrive under irrigation, but are very inferior to 
alfalfa in this respect. Clover does well under irrigation, but pro- 
duces much less hav than alfalfa. 

The sugar beet is one of the most profitable of irrigated crops. 
It prefers a deep clay loam soil and dry summers. Three to five 
irrigations are sufficient and on some soils only two are deemed 
necessary. From four to six inches are applied at each irrigation. 

Potatoes are a very important crop on irrigated land. Their 
water requirements are somewhat like sugar beets. The furrow 
method is practiced. Fifteen to twentv-four inches of water should 
be sufficient. 

Peas, beans, melons, tomatoes, onions, cotton, and manv 
other crops may be grown very successfullv under irrigation. 

Fruits of nearly all kinds may be gro'wn where climatic con- 
ditions are right. 

Irrigation in Humid Climates. — An annual precipitation of 



l!70 SOIL PHYSICS AND MANAGEMENT 

oO iuehes or more gives suttioiout moisture for producing fair crops 
of nearly all kinds if the rainfall is distributed properly. Drouthy 
periods are quite common. At Columbia. S. C, ti".' lif teen-day 
periods with less than one inch of rainfall during the growing 
season, April to October, occurred from 1900-1909. At Yineland. 
X. J., 415 periods, at Oshkosh. Wis.. "2T periods, and at Ames, Iowa, 
33 similar periods occurred during the same time. At the Illinois 
Station from 190li-19lo there were 49 periods of drouth 15 days 
long, while ll> were more than "Jo days and six more than 30 days 
in length. 

While this uneven disn-iburiou indicates that irrigation might 
be practiced during some years with protit. it is very doubtfnl. how- 
ever, whether it will ever be profitable for the ordinary cereals. A 
four-year rotation ' of corn, oats, and clover was followed on brown 
silt loam, the common prairie soil of the corn belt, for 10 years. 
Without irrigation a ten-year average yield was 43.5 bushels, while 
adjoining plots, irrigated when necessary, gave a yield of 49.9 
bushels per acre, an increase of G.4 bushels. During the dry seasons 
of 1911. 1913 and 1914 the yield of corn averaged 32.3 bushels 
without and oO.S bushels with irrigation, an increase of 18.5 bushels. 
Even with this large increase for dry seasons the average increase 
is insufficient to pay for irrigation. 

Irrigation of truck and some fruit crops, without doubt, could 
be practiced profitably, and in general the more valuable the crop 
the more profitable irrigation becomes. Strawberries and bush 
fruits respond well to irrigation, both with a finer quality of fruit 
and a longer fruiting period. 

QUESTIONS 

1. Upon what factors does the protii troni irrigation depend! 

2. Why is the irrigable area so limited? 

3. Look up some of the projects given in the table on page 257. 

4. What are the sotiroes of irrigation water? 

5. What preparation is necessi\ry before the land can be irrigated? 

6. Why should not saline water be used for irrigation? 

7. Is the sediment carried in suspension detrimental or not? If bene- 

ficial, why? 
S. What are the advantages and disadvantages of irrigation when the 

crop is not growing? 
9. INlav too much water be tised in irrigation? 

10. What is meant by the "duty of water"? 

11. What is a second-foot of water? 

12. What is the absolute duty of water? How is it expressed? 

13. How much will a second-foot irrigate? 

14. What causes this variation? 



IRRIGATION 277 

15. How much water should he applied to a crop? 

IG. Study carefully the proportionate? increase of yield for increase*! appli- 

catijon of water in the table on page 2G4, 
17. Compare the yield per acre where 7.5 inches were applied with tlia-t for 

30 inches. JJid the large applif^ation paj'? 
IS. How is water lost frf>m the irrigation canalis'' 

19. What is the significance of this loss? 

20. How is this loss prevented? 

21. How is the water mf-a-^urcfl? 

22. What are the advantages and objections to surface sprinkling? 

23. What is check-flofxling? 

24. Give advantages of furrow irrigation. 

25. Why should the irrigated land be cultivated soon after irrigation? 

26. Under what conditions is irrigation in humid climates prc^taltle? 

REFERENCES 

*Widt5oe, J. A., Principles of Irrigation Practice, 1911, p. 90. 

* Forbes, R. H., Bulletin 44, Arizona .Station, The Kiver Irrigating Waters 

of Arizona, 1902, p. 160. 
» Widtsoe, .J. A., Bulletin 116, Utah Station, The Production of Dry flatter 

with Different Quantities of Irrigation \\'ater, 1912. Widtsoe, -J. A,, 

and Merrill, L. A., Bulletin 117, Utah Station, The Yields of Crops 

with Different t/uantities of Irrigation Water, 1912. 
^Bulletin 117, Utah, Op. Cit., p. 115.' 

'Widtsoe, .J. A., Principles of Irrigation Practice, 1911, p. 3.37. 
'Widtsoe, .J, A., Principles of Irrigation Practice. 1911, p. 331. 
^Mosier, .J. G., and Gustafson, A. F., Bulletin 181, Illinois Station, Soil 

Moisture and Tillage for Com, 1915. 

General References. — ^Fortier, Samuel, Yearbook U. S. D. A., Methods 
of Applying Water. 1009. p. 293. McLaughlin, W. W., Farmers' Bulletin 
399, U. S. D. -A., Irrigation of Grain, 1910. 'Welsh, .J. S.. Bulletin 74, Idaho 
Station, Irrigation Practice, 1914. Roedinjr, F. W.. Farmers' Bulletin 392, 
U. S. D. A., Irrigation of Sugar Beets, 1910. Xewell. F. H.. Irrigation, 
1906. 



T!TTAF1"F.|{ XX 1 1 

ALKALI LANDS AND THEIR RECLAMATION 

Alkai.i lands are found in all regions of delicieni I'ainfali. Tliey 
usually occur where the rainfall is less than 30 inches, hut in India 
alkali lands exist even with a rainfall of 28 inches. The effective- 
ness of rainfall in removing alkali depends upon its character. If 
the rainfall conies in very heavy showers, as is the case in India, 
nincli will run off the surface without entering the soil, and hence 
will do little toward removing the alkali. A small rainfall coming 
as gentle showers so that it will enter the soil will he more effective. 

'^^I'he effect, too, of the rainfall depends somewhat upon the char- 
acter of the soil. Kainfnll will penetrate a loose, sandy loam soil 
much more readily than a clay. Hence, under the same rainfall a 
clay soil or a clay loam soil may contain alkali, while the sandy loam 
or sand would he free from it. 'I'lu- amount of evaporation, too, 
plays a somewhat important part in the amount present. Under 
conditions of great evaporation the alkali may be brought to the sur- 
face, while with less evaporation, as in a more northern climate, the 
alkali would not he troublesome at all. 

Alkali does not usually occur in hill lands, although in small 
level ■ valleys among hills alkali may ho I'ouiul in considerable 
amounts. It occurs abundantly in level uplands if the drainage is 
in any way interfered with. Alluvial lands frequently contain 
alkali, due to seepage from the U])land and also from the water of 
the stream. 

The Origin of Alkali. — In the decomposition of rocks and the 
further decomposition of soil material, many soluble substances are 
formed which may not be leached out by the small rainfall of the 
r(>gion but may be brought to the surface by capillary movement. 
Many of the stratified rocks contained much salt, due to the fact 
that they were formed in salt or l)rackish waters. When these be- 
came dry land the salt was leached out later and carried into tem- 
porary lakes. This accumulation continued and ultimately the 
lake became dry and a deposit of alkali was left (Fig. 127). Salt 
springs sometimes occur, the waters of which carry considerable 
amounts of alkali into depressions, where they may accumulate in 
large quantities. Whatever the source of the alkali, its existence 
278 



ALKALI LANDS AND THEIR RECLAMATION 



279 



is usually duo to cliinatic conditions. It naturally results from a 
rainfall insufficient to carry soluble material out of the soil, which 
ultimately becomes so impregnated with it as to be unproduc- 
tive (Fig. 128). 




^ ..>i2i _ _' _ ^-.'•_^^'^ ,.2.^:r:m^ 

Fig 127 — Beginning of an alkali spot (U S. Dept. of Agriculture.) 



1 




: ^;=-^.....~-«**»«-«*^. 




■HMMpHI 


'^^HNB 


iut-Jpik .,-, 5P^ ■ •»■ -^BBP 




fH^^-r ' .. 


'~...'s- '"' 




.^L^'lh^^ jJI 


■p. 




-■..."■•: ja 


IHk'' ""\JiH 


i * • 








^#'^<v » 


,V"' 1 ■ 


'*.« 




■'m,- ■** .;. 


'amr 






«f- 




j^%:^4- ' 


■.,..'. 


►:■ 


■4«mm 




*,. 


ikL^ 






V .:-:-.^: 



Fig. i2S, — Alkali area showing the absence of vegetation. (IT. S. Dcpt. of Agriculture.) 



280 



SOIL PHYSICS AND :^IANAGEMEXT 



Kinds of Alkali. — The alkalies of arid regions are commonly 
classilied as black, white, and b^o^^"u. The black consists of forms of 
sodium carbonate, which owe their name to the color produced by 
the solution of organic matter and its deposition on soil particles 
during evaporation. There are at least two forms of sodium car- 
bonate included in the black alkali, the bicarbonate (HXaCOg) and 
the normal carbonate (XaoCOg). 

The white alkalies are composed mainly of common salt (XaCl) 
and sodium sulfate (XaoSO^). together with some magnesium sul- 
fate (ilgSO^), potassium chloride (KCl), magnesium chloride 
(MgCl.,) and small amounts of many others. The brown alkali 
consists of nitrates, which are found only occasionally in damag- 
ing quantities. Different alkalies usually occur as mixture^ in 
various and indefinite proportions. A careful study of the follow- 
ing table shows this fact. That from Kern county, number one, 
contains sodium sulfate principally, but with some potassium sul- 
fate : number two, sodiimi sulfate and chloride with some nitrate ; 
number three contains sodium and potassium carbonate or black 
alkali largely: while four is a mixture of sodium sulfate, chloride, 
carbonate, and nitrate. 

Percentnge Composition of Some Typical Alkali Salts ^ (Hilgard) 



i Kern 
j County, 
1 California 


Meagher 
County, 
Montana 


Kittitas 
County, 
Washing- 
ton 


Tulare 
County, 
California 


Potash 

Soda 

Tjime 

iSIagnesia . 


5.14 
36.99 
0.15 
0.23 
0.30 
51.23 
0.29 
0.23 

'6!69 
1.34 

4.07 


1.18 

39.56 

2.86 

1.31 

34^97 

15.40 

1.19 

5.37 

' 0'.05 
j 1.29 


9.58 

45.59 

0.03 

i 0.07 
0.04 
0.09 
0.99 

; 34.93 

' I'.Oo 
0.S2 
7.03 


1.76 
38.39 


Ferric oxid^ and alumina 




Sulfuric acid 


13.20 


Chlorine 

Carbonic acid 


7.40 
1 11.62 


Xitric acid 


10.50 


Phosphoric acid 

Silica 

Organic matter and water 


1.05 
17^32 







The amount of the different kinds of alkali is not constant, but 
changes from week to week. 

Effect on Physical Condition of the Soil. — The black alkali 
deflocculates the soil, producing a puddled condition due to the 
solution of the organic matter. A very close rearrangement of the 
particles occurs by which the soil becomes impervious to water and 
practically untillable. This closer arrangement of particles de- 



ALKALI LANDS AND THEIR RECLAMATION 



281 



creases the volume, producing a slight depression in which water is 
likely to stand. It also tends to form tough and impervious strata 
at different depths in the soil. 

The white alkalies have no injurious efEect on the soil, but, on 
the other hand, tend to produce a granular character that is very 
favorable to tilth. 

Vertical and Horizontal Distribution.— The distribution of 
alkali salts is very irregular, l^oth in amount and kind. The follow- 
ing table gives the vertical distribution in one place, which may be 
somewhat rej^resentative of most alkali areas. There is a zone of 
greatest concentration at about the depth of annual percolation. 
This zone is moved dovmward slightly by the winter and spring 
rains and is brought upward hj summer evaporation. In heavy soils 
it will be nearer the surface than in permeable ones. 

Vertical Distribution of Alkali Before and After Irrigation at Various Depths, 
Tulare, California. Pounds per Acre (Hilgard.-) 





Natural soi] 


, unirrigated 


Bare land, irri- 
gated four years 


to 6 inches 

6 to 12 inches 


May 3, 1895 

350 

460 
1350 
3160 
7530 
9550 
3380 
1300 


September, 1895 

420 

440 
1710 
4450 
7810 
8120 
1780 

690 


May, 1895 

12220 

7540 


12 to 18 inches 


6180 


18 to 24 inches 


3320 


24 to 30 inches 


1380 


30 to 36 inches 

36 to 42 inches 


760 
530 


42 to 48 inches . . 


500 







The amount of alkali in an area or even in a small field varies 
almost infijiitely. It seems to move from place to place, so that an 
area with abundant alkali ma}^ in short time, perhaps not over a 
week or two. have much less. Tlie kind of alkali varies even more 
than the quantit}-. A sj)ot of black alkali may change to white, and 
vice versa. Low places in irrigated land will usually contain most 
alkali, and are frequently called alkali marshes. 

Effect of Irrigation on Rise of Alkali. — The tendency of irri- 
gation is to increase the amount of evaporation from the surface 
of the soil. The water applied enters the soil, dissolves the salts and 
carries them downward. TVlien evaporation begins the water moves 
upward, carrying the salts with it and depositing them at the sur- 
face. The effect of successive irri2:ations and the excessive evapora- 
tion that follows is to transfer large quantities of salts to the sur- 



282 



SOIL PHYSICS AXD MANAGEMENT 



face foot of soil. This is spoken of as the '' rise of alkali '' and the 
efEect is to ruin the land for ordinary crops. The result is well 
shown in the table on page 281, where the surface foot contained 
19,760 pounds, while the same depth under natural conditions con- 
tained 860 pounds. 

Amount and Composition of Salts in Alkali Spot from Center to Circumference, 
4 Feet Apart and 1 Foot Deep ^ 





1 Center of 


Four 


Eight 


Twelve 


Outer 


Mineral salts 


1 spot 


feet 


feet 


feet 


margin 


Potassium sulfate 


. . . ' 6.70 


9.55 


11.92 


19.26 


13.95 


Sodium sulfate 


. . . 19.84 


12.85 
.07 


23.72 
.95 


23.97 
2.05 


16.96 


Magnesimn sulfate 


3.07 


8.29 


Sodimn chlorid 


. . . 13.80 


23.73 


24.12 


24.23 


29.69 


Sodium carbonate .... 


. .. 50.72 


50.96 


37.55 


35.49 


29.94 


Sodium phosphate .... 


. .. 5.57 


2.88 


.87 




1.04 


Sodium nitrate 


.30 




.87 




.13 



The irrigation canals and ditches sometimes pass through a 
lather open soil that permits considerable seepage. It is estimated 
that 30 per cent of the water taken in at the headgates is lost by 
seepage from the canals themselves and another third is gone before 
it is used for irrigation. 

This seepage water passes through the soil, dissolving the alkali, 
and finally both water and alkali come to the surface in some slightly 
lower place in the field. This alkaline water gives rise to alkali 
marshes which, although very small at first, gradually increase in 
size until much of the land is affected. The " rise of alkali " has 
ruined large amounts of land because of the excessive use of irriga- 
tion water. The desire of farmers to get their " money's worth " of 
water has hastened their ruin. 

Effect of Alkali on Plants. — A few plants have become adapted 
to growing where large amounts of alkali are present and are in- 
jured only when the soil becomes very strongly alkaline. There are 
small local areas where the alkali is sufficient to kill all vegetation. 
As a general rule, these alkali-resistant plants are not of much eco- 
nomic importance. 

As a result of this poisoning, cultivated plants are injured to 
varying degrees (Fig. 129). Where the alkali is very strong the 
plants show a sickly growth and finally die without fruiting. If 
less in amount they may become dwarfed and produce rather 
scantily. Affected trees show a scanty leafage with small fruiting. 

The external injury done to plants is confined to a narrow zone 



ALKALI LANDS AND THEIR RECLAIMATIOX 283 




284 



SOILS PHYSICS AND MANAGEMENT 



at the surface of the soil or near the root erowu. The bark is 
turned to a brown or bhick color for about a half inch and may 
easily be peeled oft'. In other words, the plant has been " girdled." 
If the plant does not die it becomes unprofitable. 

The roots are not injured perceptibly to any depth, as a general 
rule, but it is very likely that the entire plant is poisoned more or 
less. It is only where common salt is very abundant in the subsoil 
that the deeper roots are injured. 

Limit for Germination and Growth. — Germinating plants are 
most sensitive to alkali, hence a comparatively small amount in the 

Highest Amount of Alkali in Which Plants Were Found Unaffected* — Arranged 
from Highest to Lowest. Pounds Per Acre Four Feet Deep 



Sulfates 
(Glauber'ssalt) 



Carbonate 
(sal soda) 



Chloride 
(common salt) 



Total 
alkali 



Saltgrass 

Saltbush .... 
Alfalfa, old . . . 

Sorehiim 

Radish 

Sugar beet 

Grapes 

Onions 

Potatoes 

Barley 

Gluten wheat . 

Oranges 

Wheat 

Apples 

Celery 

Alfalfa, young. 

Rye 

Date palm .... 



44,000 
125,640 
102,480 
61,840 
51.880 
52,640 
40,800 



12,020 

20,960 

18,600 

15,120 

14,240 

4,080 

11,120 

9,800 

5.. 500 



136,270 
18.560 
2,360 
9,840 
8,720 
4,000 
7,550 



12,170 

3,000 

3,840 

1,480 

640 



960 

2,800 



70,360 
12,520 

' 9^680 
2,240 

10,240 
9,640 
5,810 
5,810 
5,100 
1,480 
3,360 
1,160 
1,240 
9,600 

'ij26 



381,110 
156,720 
110,320 
81,360 
62.840 
59,840 
45,760 
38.480 
38,480 
25.520 
24,320 
21,840 
17,280 
16,120 
13,680 
13,120 
12.480 
S,32S 



surface soil at that period may produce very serious results. As an 
illustration, young alfalfa will not stand more than 13.000 pounds 
of alkali in the soil to a depth of four feet, while old alfalfa will 
flourish where nearly ten times that amount exists, and this is true 
more or less of all plants. 

In the growing of certain crops special methods are employed 
for reducing the amount of alkali in the surface soil until the plant 
becomes old enough to resist its effect. All plants are not equally 
injured by the same amount of alkali. Some will grow and flourish 
where others will die. In the case of the tussock grass, it wdll grow 
where the soil to a depth of four feet contains 499,000 pounds of 



ALKALI LANDS AND THEIR RECLAMATION 285 

alkali, while 7000 or 8000 pounds will injure the lemon tree. The 
preceding table gives the highest amount of alkali in which plants 
were found unaffected. 

As a general rule plants cannot withstand more than 0.1 per cent 
of sodium carbonate or 16,000 pounds in a depth of 4 feet, 0.25 per 
cent or 40,000 pounds of sodium chloride or common salt, nor 
more than 0..5 jDer cent or 80,000 pounds of sodium sulfate. If the 
amounts increase to any extent beyond these, the plants are very 
seriously injured. 

Utilization and Reclamation of Alkali Lands, — The large 
extent and great value of alkali lands make their utilization and 
reclamation some of the most important problems in irrigated 
regions. While a great many methods have l^een tried with partial 
success, yet the removal of the alkali is the only remedy that will 
permanently reclaim the land. It may be well to notice some of 
the more or less temporary expedients for utilizing these soils. 

1. Growing Alkali-Resistant Crops. — All plants are not 
equally sensitive to alkali, and the proljlem here is to find the crop 
of highest value, that will be affected least by the salts. The salt 
grass and salt bushes grow under extreme conditions and they are 
of considerable value for forage. >Sweet clover (Melilot) grows 
well where alkali is quite abundant and furnishes very good pasture 
and forage when cut early. In some places it is crowding out other 
plants. For gaining the requisite knowledge, the kinds and amounts 
of each alkali must be determined and different crops grown to learn 
the effects of varying quantities of salts upon them. After getting 
this information the determination of the alkali of new lands will 
give a very good idea of the crops to grow. Many plants are most 
sensitive to alkali when young and some special precautions must 
be taken in starting them. As a general rule shallow rooting crops 
are more sensitive than the deeper rooting ones, such as alfalfa and 
melilot, whose roots extend beyond the zone of greatest concen- 
tration. 

2. Retarding Evaporation. — Alkali salts do most of their in- 
jury when near the surface. They are brought there by the upward 
movement and evaporation of water, and anything that will prevent 
this will retard the accumulation of salts in the zone of greatest 
injur3^ This may be done in two ways — by mulching and shading. 
The efficiency of a layer of soil in fine tilth to prevent evaporation 
has already been discussed. This should be three or four inches 



286 SOIL PHYSICS AND MANAGEMENT 

deep to be most effective (Fig. 130). This mulch if maintained 
will prevent excessive capillary movement until the crop is suffi- 
ciently large to shade the ground. The maintenance of the mulch 
then becomes of less importance. Alfalfa during three-fourths of 
the time of its growth furnishes a very effective shade. Evaporation 
from soil of orchards is prevented very materially by the shading of 
the trees. Artificial mulches, as straw, leaves, sawdust, and manure, 
may be used, but are too expensive for large areas and only possible 
for high-priced crops under a very intensive system of agriculture. 
3. Deep Plowing and Turning Under Alkali. — The practice 
of encouraging evaporation is sometimes resorted to for bringing 
the alkali to the surface and then turning under so deeply that it 




Fig. 130. — An orchard well cultivated prevents the rise of alkali. (U. S. Reclamation 

Service.) 

will not rise to the surface until after the young crop has passed 
through its most sensitive stage. By this means alfalfa and other 
crops may be started. When the crop attains such size that it shades 
the soil and the roots take up the water from beneath, comparatively 
little moisture evaporates from the surface and the alkali is not 
carried up to any extent. 

4. Neutralizing Black Alkali. — The black alkali when present 
in amounts of one-tenth of a per cent prevents the growing of most 
crops. Sodium sulfate may be present in amounts five times as 
great before it becomes injurious. By treating the black alkali 
spots with gypsum (land plaster) a chemical reaction takes place 
when moisture is present, producing sodium sulfate and calcium 
carbonate. The former is not sufficiently soluble to be injurious, 



ALKALI LANDS AND THEIR RECLAMATION 287 

while the latter is very beneficial to the soil in its puddled condi- 
tion. The reaction is as follows : 

I^aXOg -f- CaSO^ = JsTa^SO^ + CaCOg. 

The amount to be applied depends upon the amount of alkali 
present. Twice as much gypsum as black alkali is needed, but it is 
best to apply 200 to- 400 pounds per acre annually. Moisture is 
necessary for the reaction to take place. The change in the phy- 
sical condition of the soil is as important as the chemical effect. The 
impervious soil begins to swell up, becomes porous and soon the de- 
pressed spot is brought to the general level. 

5. Removing the Salts from the Soil. — The removal of the 
salts is the only permanent remedy for reclaiming alkali lands. 
This is accomplished in several ways. 

(a) By Scraping. — When excessive evaj)oration has brought 
large quantities of alkali to the surface it may be scraped off with 
two or three inches of soil and thrown into drainage systems that 
will carry them off the land. Large amounts of alkali may be re- 
moved in this way, but this applies to small areas only. 

(b) Flooding. — The alkali may be leached downward into the 
soil to a depth of three or four feet by flooding so that the crop may 
be temporarily relieved from any danger of injur}^ Attempts have 
been made to wash the salts off the land, but since they soak into 
the soil as soon as dissolved this is impossible. 

(c) By Cropping. — ^This method is to produce crops that take 
up large amounts of alkali in their growth which will be removed 
with the crop. The Australian salt bush when mature contains 20 
per cent of ash and yields as much as five tons per acre. A single 
crop will remove approximately a ton of alkali. 

(d) Under drainage.- — Leaching out the salts through under- 
drainage is the most practical and permanent remedy that has been 
devised. This, of course, requires a thorough drainage system as 
complete as for draining the swamps of humid regions. After the 
drainage system is installed, the soil must be flooded to leach out 
a large per cent of the salts, so that there will be little danger from 
alkali later. Tliis requires a large amount of water, as the flooding 
must continue for several months (Fig. 131). With every irriga- 
tion system a corresponding underdrainage svstem should be in- 
stalled to carry off the water from excessive irrigation and seepage, 
which is largely responsible for the rise of alkali. 

To give an idea of the way reclamation is accomplished by 



288 



SOILS PHYSICS AND MANAGEMENT 




ALKAIJ LANDS AND THEIR RECLAMATION 



289 



leaching let us consider briefly the work on a 40-acre tract reclaimed 
near Salt Lake City. The soil was badly affected by alkali, there 
being from 3.5 to 5 per cent to a depth of four feet. The salts 
were principally sodium ehlorid and sodium sulfate, and since 0.25 
per cent of the former and 0.5 per cent of the latter represent the 
ujjper limit of resistance of most farm crops it will be seen that the 
land was worthless. 

The work began in 1903, the Bureau of Soils and Utah Station 
cooperating.^ A system of underdrainage was installed, the laterals 
being three-inch and four-inch tiles, 150 feet apart and placed four 
feet deep. The soil was a sandy and silty loam from 13 to 18 




FiQ. 132. — Wheat on reclaimed alkali land near Fresno, Cal. Reclaimed by one year of 
flooding with underdrainage. (U. S. Dept. Agr.) 

inches deep; the underlying material varied from heavy loam to 
clay. The total volume of water used in flooding was 17,896,866 
cubic feet or 10.3 feet deep over the 40 acres. The total salts re- 
moved in the 8,775,940 cubic feet of drainage water was 10,634,000 
pounds of 5317 tons, or about one and one-fourth pounds per cubic 
foot of water. The amount of alkali in the soil at the beginning 
was 6651 tons. About 80 per cent was removed. 

The cost of installing the drainage system was $16.50 per acre. 

A 30-acre tract at Fresno, California, was reclaimed in a similar 

way, the cost of installing the drainage system being the same as 

for the Utah area (Fig. 133). This land had been purchased for 

$350 per acre and was abandoned 10 years after its purchase. 

19 



290 SOIL PHYSICS AND MANAGEMENT 

Flooding was begun on March 1, 1903, and in Xovember, 1903, 
alfalfa was seeded on three acres, which was cut six times the next 
year, producing a total of 25,000 pounds of alfalfa hay. 

Other tracts, Xorth Yakima, Washington, Billings, Montana, 
and Tempe, Arizona, were reclaimed. The cost of installing the 
drainage system varied from $21 to $35 per acre. 

Hardpan. — Where hardpan occurs in the subsoil reclamation is 
a much more difficult process. This layer usually varies in depth 
from one to four feet or even more. The cementing material may 
be calcium carbonate, iron compounds or other substances and may 
be from a few inches to several feet in thickness. In some instances 
the action of the water is to disintegrate the hardpan, and where 
this occurs little difficulty is caused by it. Calcium carbonate some- 
times acts in this way. Usually this does not occur and it becomes 
practically impossible to leach out the alkali because the hardpan 
will not permit the water to pass downward. The alkali may be 
leached to the depth of the hardpan, but much of it remains in this 
stratum and soon rises. If the hardpan is due to black alkali it is 
necessary to neutralize this with g\'psum before flooding. 

Most soils, especially silt loams, clay loams, and clays, are 
injured more or less by flooding. The granules are destroyed, so 
that when the water is removed the soil bakes or is partly puddled, 
and it becomes necessary to use some means for restoring the tilth. 
This may be accomplished by turning under a green manure crop 
or by an application of farmyard manure. 

Value of Alkali Land. — Alkali lands include some of the most 
valuable lands in the West, but more especially those that are 
capable of being irrigated. They are worthless as they are, but 
after the alkali is removed they have a very high value. Where 
water may be had in abundance the cost of reclaiming is not exces- 
sive. In doing this reclamation work drainage districts should be 
organized similar to those in humid regions for draining swamp 
land. The expense would in this way be reduced to a reasonable 
amount per acre. 

Alkali Soils of Humid Regions. — In areas where the rainfall 
would seem to preclude the possibility of alkali, soils are sometimes 
found to contain considerable amounts of soluble material. 

Dorsev ® speaks of the patches of alkali at the ^Maryland Station, 
where a thin layer of soil showed 1.83 per cent of water-soluble salts, 
such as nitrates of calcium, magnesium, sodium, and potassium, 
together with some chlorides and sulfates. 



ALKALI LANDS AND THEIR RECLAMATION 291 

Small spots a few rods in diameter occur iu southern Illinois in 
which the soluble salts form a deposit that looks like a heavy 
white frost or light snow. Analysis shows this to be sodium sulfate. 
It has been brought to the surface by seepage from higher land. 

In the glaciated area, of the Middle West alkali soils occur in 
many low, swampy places, usually in small patches of a few square 
rods, but in some cases extend over many acres. During dry spells 
whitish incrustations appear on the surface of the soil that disap- 
pear with rains (Fig. 133). These alkali areas almost always eon- 




FiG. 133. — A dwarfed bushy or leafy corn plant growing on alkali soil of humid area. 
Shells are nearly always indications of alkali. 

tain large quantities of magnesium carbonate, and when this com- 
2)ound amounts to more than one per cent crops such as corn and 
oats are badly affected. The corn does not grow well, and where 
strongly impregnated with the carbonate is bushy and the blades 
turn brown or reddish. If a smaller amount is present the blades 
are strij^ed with yellow. Very little grain is produced. Oats 
make a rank growth, but almost invariably lodge. 

Drainage is the ultimate remedy, but the process is slow Avhen 
onl}^ the natural rainfall is depended upon. 



292 SOIL PHYSICS AND MANAGEMENT 

However, for immediately correcting the effect of the alkali 
applications of from 75 to 200 pounds of potassium salts may be 
used when they can be obtained at reasonable prices (Fig. 194). 
Coarse stable manure is as efficient as potassium salts, and even 
straw or green manure turned under has a. very beneficial effect. 

QUESTIONS 

1. What conditions give rise to alkali soils? 

2. On what kind of lands as to topography is alkali most abundant? 

3. What is the source of the alkali salts? 

4. What is the composition of black alkali? 

5. What salts constitute the white alkali ? 

6. Note effects of black alkali upon the soil and organic matter. 

7. How many pounds of alkali in the surface foot of soil in each column 

in the table of page 282 ? 

8. How does irrigation cause a rise of alkali? 

9. What are " alkali marshes "? 

10. What is the first effect of alkali on plants? 

11. What is the nature of the effect of alkali upon trees? 

12. Is the effect of alkali the same on all plants? 

13. What effect does alkali have on germination? 

14. Why are shallow rooted crops more affected by alkali? 

15. What methods are adopted for preventing evaporation? 

16. What means are taken to start crops whose young plants are very 

sensitive to alkali ? 

17. How is black alkali neutralized? 

18. What objections to removal of alkali by scraping? 

19. Why l?annot alkali be washed off of land? 

20. How may the Australian salt bush be used to remove alkali? Does 

this plant have any value? 

21. Describe the reclamation of the Utah tract. 

22. What percentage of the water applied was carried off by drainage? 

23. Why is a hardpan detrimental iii removing alkali ? 

24. What is the effect of flooding on tilth? How may the condition be 

corrected ? 

25. What is the importance of reclamation of alkali lands from an economic 

standpoint ? 

26. Why do alkali soils occur in humid regions? How does the alkali differ 

from that of arid regions? 

27. What is the substance that does the injury? 

28. How is corn affected by magnesium carbonate ? 

29. What are the remedies to be used? 

REFERENCES 

^ Hilgard, E. W., Soils, 1906, pp. 442-43. 

^Hilgard, E. W., Report of California Station, 1894-95. 

=> Op. Cit., p. 449. 

*0p. Cit., p. 467. 

' Dorsev, C. W., Bulletin 35, Bureau of Plant Industrv, U. S. D. A., Alkali 

Soils of the United States, 1906, pp. 174-194. 
«0p. Cit., p. 157. 



CHAPTEEXXIII 

TEMPERATURE 

The vital functions of j^lants require a certain temperature for 
their best performance. Plants may grow at other temperatures, but 
the}^ grow most vigorously at the optimum temperature, which for 
different plants varies from 80 to 100 degrees F. Below this growth 
diminishes till at about -10 degrees F. it ceases for most plants. At 
temperatures higher than the optimum growth is less vigorous till a 
point is reached at from 99 to 115 degrees F., where it practically 
ceases. A knowledge of the functions of heat in relation to germi- 
nation, growth, physical phenomena, and bacterial activit}^ and the 
means of its control, is of considerable practical importance to the 
agriculturist. 

The Sources of Soil Heat. — 1. Direct Radiation from the 
Sun. — The sun gives off both light and heat rays, and some of the 
latter, striking the earth, are absorbed. This is the chief source 
of heat. The amount received from the sun is enormous. Lang- 
ley gives it as equal to 1,000,000 calories per hour per square 
meter of surface from a vertical sun in a clear sky. If all of this 
energy were absorbed by the plowed six inches of soil on a square 
foot its temperature would be raised by 24.5 degrees in an hour. 
The soil is always radiating heat, consisting of waves of lower pitch. 
These are easily held by glass or water vapor, which is transparent 
to waves of higher j)itch or refrangibility. Hence the excessive heat 
of the glass house and the oppressive heat when the air is laden 
with moisture in the summer. 

The heat received by any part of the earth's surface from the 
sun depends upon the transparency of the atmosphere to heat. Dust 
particles and water vapor in the atmosphere intercept some, while 
dry air, free from dust, absorbs very little. 

Comparing the highest temperature reached by a blackened 
thermometer in vacuo at Greenwich, England, near sea level, and at 
Davos, Switzerland, 5400 feet above sea level, the temperature at 
the latter place was 20.1 degrees F. higher in November, 36.2 degrees 
in December, 37.2 degrees in January, and 24.2 degrees in Feb- 
ruary. The ground was continuously covered with snow at Davos. 
While more heat is received from the sun at high altitude per unit 

293 



294 



SOIL PHYSICS AND MANAGEMENT 



area, it is radiated into space much more rajjidly because of the 
small amount of vapor in the air to hold it. 

2. Precipitation. — When warm rain falls upon and penetrates 
the cold soil it carries with it large amounts of heat. This may 
account for the rapid growth of plants after a shower in spring. 
An inch of rain 10 degrees warmer than the soil would raise the 
temperature of the surface six inches of soil 4.6 degrees if 10 per 
cent of moisture existed in the soil to begin with. 

3. Chemical changes in the soil result in the production of 
heat. This is especially true of all chemical changes in organic 
matter, but particularh' so of green crops and fresh farmyard 
manure. The results of some experiments at the Imperial College, 
Tokio, Japan, with different amounts of manure applied and thor- 
oughly mixed with the soil, are given for five-day intervals in the 
accompanying table: 



InfliLence of Farmyard Manure on Temperature of Soil} Degrees Fahrenheit 



Tons per acre None 10 20 40 



Temperature, October 27-31 

Excess over unmanured 

Temperature, November 1-5 . , 

Excess over unmanured 

Temperature, November 6-10 

Excess over unmanured 

Temperature, November 11-1.5 

Excess over unmanured 

Average excess with manure in first twenty 

days 



60.5 
58^5 
57^2 
54^7 



62.5 

2.0 
59.5 

1.0 
57.8 

0.6 
54.8 

0.1 

0.93 



63.8 

3.3 
60.2 

1.7 
58.4 

1.2 
.55.3 

0.6 

1.70 



2.25 



80 



65.1 

4.6 
62.2 

3.7 
60.4 

3.2 
56.8 

2.1 

3.40 



It will be noted that the heavier the application the greater the 
increase in temperature. 

4. Physical Changes. — When a soil absorbs water its tempera- 
ture is increased. This is true for both water vapor and liquid 
water, the former producing the highest temperature because of the 



Increase in Temperature hy Absorption of Water Vapor at 86 Degrees F. 
[SO Degrees CY 

Quartz sand 1.58° F. ( 0.88° C.) 

Calcium carbonate (precipitated) 2.64° F. ( 1.47° C.) 

Kaolin 4.73° F. ( 2.63° C.) 

Hydrated ferric oxide 16.74° F. ( 9..30° C.) 

Peat 22.05° F. (12.2.5° C.) 



TEMPERATURE 295 

latent heat given off during condensation. The greater the hygro- 
scopic capacity of the soil the higher is the temperature produced. 

From the preceding tahle on page 294 it will he seen that peat 
and ferric oxide gave the highest temperature, while quartz sand, 
with its low hygroscopic capacity, gave the least increase. In 
the next table the increases are not so large. 

Increase of Temperature by the Application of Liquid Water at 50 Degrees F . 

{10 Degrees C.)^ 

Quartz sand 18° F. ( .10° C.) 

Calcium carbonate (precipitated) 50° F. ( .28° C.) 

Kaolin 1 49° F. ( .83° C.) 

Hydrated ferric oxide ■ 11.88° F. (6.60° C.) 

Loss of Heat. — While the soil is receiying heat through these 
various sources it is losing it in several different ways. 

1. By Radiation. — The amount of heat radiated from soils is 
not directly aft'ected by their color. The statement is made in 
physics that good absorbers are good radiators. This is also true 
that the heat lost by radiation and convection b}' one body to another 
surrounding it is proportional to the temperature difference between 
the two. Dark soils are good absorbers of the sun's heat, but they 
have no tendency to lose it more raj)idly because of their color, but 
because they are warmer than poor absorbers or light colored soils, 
and at night the}' all tend to cool to the temjjerature of the sur- 
rounding atmosphere. Black soils having absorbed more heat will 
have more to radiate, but there is no tendency for dark soils to 
become lower in temperature at night than light-colored ones under 
the same conditions. 

In order to determine the effect of color on radiation Bouyoucos 
colored white sand and determined the radiation ratio as given in 
the following table : 

The Radiatwn Ratio of Different Colored Sands 



Colored sand 


Radiation ratio 


White . .. ... 


1.060 


Black 


1.051 


Blue 


1.045 


Green 


1.040 


Red 


1.050 


Yellow 


1.048 



296 SOIL PHYSICS AND MANAGEMENT 

The results seem to indicate that radiation is slightly better from 
white sand, but. the differences are so small that they come within 
the experimental error, and so the conclusion is reached by the 
experimenter that color does not affect radiation. A large amount 
of the heat radiated from the soil is brought to the surface by con- 
duction. It is absorbed during the day and is conducted downward 
to a depth of from one to twelve inches. As the temperature of the 
air becomes lower at night the heat in part is conducted back to the 
surface and is radiated into the air. From February to August 
more heat is received by the soil than is radiated from it, but during 
the rest of the year radiation is greater than absorption, and as a 
result the temperature of the soil is becoming lower. (See the 
table, page 307.) 

2. By Conduction Downward Into the Soil. — The process of 
conduction is a very slow one, so slow that the soil at a depth of 
36 inches has an average annual range of only 28.7 degrees F. for a 
ten-year average, while at a depth of one inch the average range was 
45.8 degrees. Some of the heat is conducted to such a depth that it 
cannot influence the growth of plants in any way and may be con- 
sidered lost. 

3. By Evaporation of Water. — When water is evaporated large 
amounts of heat are carried away as latent heat in the vapor. 

4. By Convection Currents of Air. — The heated soil warms 
the adjacent air, causing it to expand and rise. These currents of 
warm air are constantly carrying large amounts of heat upward. 
The effect of this in comparison to radiation may be seen by placing 
thermometers at equal distances above and on the side of a heated 
object. 

Soil Temperature for Vital Functions of Plants. — 1. Tem- 
perature for Germination. — The temperature at which ger- 
mination takes place varies with different . classes of plants. 
Slow germination in a cold soil brings about favorable con- 
ditions for the action of fungi and bacteria upon the seed which may 
cause decay. Some of our cultivated crops, as corn and beans, are 
especially susceptible to injury in this way. This may bring about 
a low percentage of germination and a poor stand results. Uloth ^ 
found that certain seeds, one of which was wheat, would germinate 
in a dark cellar on a cake of ice, the rootlets descending into the ice 
to a slight depth by melting cylindrical cavities. The rootlets of 
Norway maple descended into the ice tx) a depth of 7.5 centimeters. 
The next table gives the minimum, optimum, and maximum tem- 
perature at which germination takes place. 



TEMPERATURE 



297 



Minimum, Optimum, and Maximum Temperatures for Germination of Various 
Seeds as Determined by Different Investigators {Degrees Fahrenheit) 





Minimum 


Optimum 


Maximum 


Investigator 


Sachs 


Van 
Tieg- 
ham 


Haber- 
landt 


Sachs 


Van 
Tieg- 
ham 


Haber- 
landt 


Sachs 


Van 

Tieg- 

ham 


Haber- 
landt 


Wheat 

Barley 

Peas 

Corn (maize) 
Red clover . . 

Turnip 

Mustard 

Melon 

Pumpkin . . . 
Oats . 


41 
41 

44.^ 
48 


) 


41 
41 
44 
49 
42 

32 , 


32-40 
32-40 
32-40 
40-51 
32-40 
32-40 
32-40 
60-65 
51-60 
32-40 


8 
8 
8 
9 


4 
4 
4 
3 


84 
83 
80 
93 
70 
89 
81 
99 


77-88 
77-88 
77-88 
88-100 
77-100 
77-88 
61-88 
88-100 
100 
77 


104 
104 
102 
115 


99 
100 

115 
82 

108 
99 


100 

100 
100 

111-122 

100-111 

88-100 

88-100 

111-122 

111-122 

88-100 



By consulting the . following table it will be seen that we 
long ago adapted our agricultural practices to conform in a measure 
to the temperature requirements of plants for germination. The 
temperatures for growth are very similar to those for germination. 

Time Required for Appearance of Radicle at Different T'emperatures * 



Temperatures 


40° F. 


51° F. 


60° F. 


65° F. 


Rye 

Wheat and barley 


4 
6 

7 
6 
6 

7.5 
7 
2 
5 
6 
8 
22 
8 


2.5 
3 

3.75 
5 

3.75 
3 

6.5 
1.5 
3 
2 
4 
9 

4.5 
11.25 


1 
2 

2.75 
2 

2.75 
1.75 
4.75 
1 

1.75 
1 
2 

3.75 
2 

3.25 
10.75 


1 

1.75 


Oats 


2 


Vetches 


2 


Alfalfa 


2 


Red clover 


1 


Beans 


4.25 


IMustard 


0.75 


Peas 


1.75 


Rape 


1 


Turnip 


1.75 


Sugar beet 


3.75 


Flax 


2 


Corn (maize) 


3 


Pumpkin 


4 







It will be seen from the preceding table that the time for germi- 
nation is controlled largely by the temperature and emphasizes the 
necessity of not seeding until the temperature is high enough. 

2. Temperature for Growth. — With most plants, and espe- 
cially Avith our cultivated ones, growth does not begin until a tern- 



298 



SOIL PHYSICS AND MANAGEMENT 



perature of 40 to 50 degrees F., the zero point of growth, is reached 
by tlie soil. Growth is most vigorous at from 80 to 90 degrees F. 
This means that the temperature must reach that point during the 
day, even if it does fall below this during the night. The amount 
of growth depends upon the proportion of the day that is above the 
zero point of growth or the heat hours. Tt will be seen from the 
following table that corn requires a medium high temper&ture before 
growth begins, while melons require a still higher one. 



Temperature of Soil for Growth " 




Crops 


Minimum 


Optimum 


Maximum 


Mustard 


32° F. 
41° F. 
41° F. 
49° F. 
49° F. 
65° F. 


81 °F. 
83.6° F. 
83.6° F. 
93.6° F. 
92.6° F. 
91.4° F. 


99 ° F. 


Barley 


99.8° F. 


Wheat 


108.5° F. 


Maize 

Kidney bean 

Melon 


115 ° F. 
115 °F. 
HI ° F. 







3. Temperatures Favorable for Osmosis and Diffusion. — 

Osmosis is a process upon which germination of seeds and the 
growth of plants depend, 'i'he seed coat is the osmotic meml)rane, 
and the rapidity with which water passes through this depends upon 
the temperature. Osmotic pressure is the power that sends the soil 
moisture into the roots of plants. At low temperatures plants may 
wilt, and Sa(;hs found that at 55 degrees F. pumpkin and tobacco 
plants did not receive sudicient moisture to compensate for even slow 
transpiration. 

Diffusion of substances in solution .is influenced by tempera- 
ture in the same way, being much more rapid at high than low 
temper;! in res. 

4. Temperatures for Nitrification. — Our ordinary crops 
depend to a large extent upon the activity of bacteria in the soil, 
which by means of the process of nitrification use the nitrogen in 
the organic matter to produce soluble nitrates. The soil bacteria do 
not work to any large extent if the temperature of the soil is below 
41 degrees F., nor above 130' degrees F. They are most active 
at temperatures between 60 and 85 degrees F. 

Conditions Affecting Soil Temperature. — 1. Specific Heat. 
— It is a very interesting as well as an important fact that the same 
amount of heat applied to different substances raises the temperature 



TEMPERATURE 



299 



unequally. Of all substances, solid or liquid, water requires the 
greatest amount of heat to change its temperature one degree. The 
quantity of heat required to change the temperature of a unit mass 
of any substance one degree is the specific heat of the substance. 
Water is taken as unity. 

Specific Heats of Some Common Substances' 



Aluminum 


0.219 


Lead 


0.305 


Brass 


0.09 


Quartz 


0.174 


Copper 


0.0936 


Silver 


0.0559 


Glass 


0.117 


Tin 


0.0552 


Granite 


...... 0.19 to 0.20 


Zinc 


0.0935 


Iron 


0.119 


Mercury 


0.0333 



This means that one pound of iron requires 0.119 as much heat 
to change its temperature one degree as is required by a pound of 
water, or that the heat necessary to effect a change of one degree in 
a pound of water would raise 8.4 pounds of iron one degree, or one 
pound 8.4 degrees. 

Dry soils generally possess a low specific heat, varying from 0.15 
to 0.3, with an average of 0.215, or, in other words, it requires from 
one-seventh to one-third as much heat to raise the temperature of dry 
soil one degree as of water. 



Specific Heat of Soil Constituents 





Lang 


Bouyoucos ' 




Equal 
weights 


Equal 
volumes 


Equal 
weights 


Equal 
volumes 


Sand 


0.189 
0.233 
0.214 
0.477 
0.163 
0.206 


0.499 
0.568 

0.587 
0.831 
0.561 


0.1929 
0.206 
0.215 
0.253 

0.2045 


509 


Clay 


569 


Loam 

Peat 

Ferric oxide 


0.551 
0.440 


Calcium carbonate 




Grave] 


0.554 



The figures for peat vary a great deal, because in some cases no 
allowance was made for the heat of wetting. The specific heat of 
equal volumes may be obtained by multiplying the specific heat of 
equal weight by the specific gravity. 



300 



SOIL PHYSICS AND MANAGEMENT 



Patten has made determinatious of the specific lieat of soil types 
of various classes as given in the following table : 

Specific Heat of Soils (Equal Weights) ' 



Norfolk sand 0.1848 

Hudson River sand 0.1769 

Fine sand (soil separate) 0.1799 

Fine quartz Hour 0.1900 

Coarse sand (quartz) 0.1900 

Podunk fine sandy loam 0.1828 

Leonardtown silt loam 0.1944 

Hagerstown loam 0.1914 

Galveston clay 0.2097 

Muck soil, 25 per cent of organic matter 0.1566 



Humus has the highest and sand the lowest specific heat of soil 
constituents. Wet soils require much more heat to raise their tem- 
perature than dry ones. In case of a dry silt loam whose specific 
heat is 0.23 if 20 per cent of moisture is added, its specific heat will 
be raised to 0.36. One hundred pounds of dry soil would require the 
application of 23 heat units to raise its temperature one degree, 
while the same weight of the wet soil would require 36 heat units. 
The latter would warm up much more slowly than the former. The 
effect of varying amounts of moisture on the specific heat is here 
shown : 

Effect oj Moisture on Specific Heat, Podunk Fine Sandy Loam i" 



Moisture content, 

per cent of dry 

weight 


Specific heat 


Moisture content, 
per cent of dry- 
weight 


Specific heat 


0.268 
1.33 
2.14 
2.83 


.1850 
.1935 
.2000 
.2053 


6.60 
10.08 
20.25 
26.93 


.2334 
.2575 
.3204 
.3562 



2. Evaporation of Water. — The temperature of soils is lowered 
by the evaporation of water from them. In the change from a solid 
to a liquid or from a liquid to a vapor heat is required to effect the 
change. When the opposite change takes place heat is liberated. 
When ice melts 80 calories (centimeter-gram system), or 1-ii heat 
units (English system), are used in producing the changes in a unit 
weight. When water passes into vapor, 537 calories or 966.6 heat 
units are required, and when condensation takes place this heat is 



TEMPERATURE 



301 



liberated. When water evaporates from a soil, the larger part of 
the heat used in the process is taken from the soil. This has a 
tendency to lower the temperature, and hence wet soils do not warm 
up rapidly in the spring and are spoken of as " late '^ soils. They 
become warm only when the greater j)art of the water has evaporated 
or when properly drained. 

If one-half pound of water is evaporated daily from a square 
foot of soil, 483.3 heat units or 121,790 calories are required, the 
larger part of which would be taken from the soil. If all of the heat 
necessary for this were taken from a cubic foot of loam soil having 
an apparent specific gravity of 1.25 and containing 20 per cent of 
moisture it would lower the temperature 15.5 degrees F. 

Clays, peats, and undrained soils are cold and late partly because 
of this evaporation. 

Anything that diminishes evaporation aids in increasing the 
temperature of soils. Mulches, windbreaks, and drainage decrease 
evaporation, and hence increase temperature. The strong winds of 
spring increase evaporation, hence tend to keep the soil cooler until 
it becomes fairly dry, when i{ warms up rapidly. 

The effect of the wind upon evaporation has been well shown 
by King, who determined the evaporation at 20, 150, and 300 feet 
to the leeward of a hedgerow. The amount was 24 and 33 per cent 
greater for 150 and 300 feet respectively than at 20 feet. When 
the air came across a field of standing clover 780 feet wide the 
evaporation was 30.1 per cent greater at 150 feet, and 40 per cent 
greater at 300 feet than at 20 feet from the field. 

3. Drainage. — The effect of drainage on temperature at differ- 
ent depths is shown in the table. The soils are the same. Drainage 

The Effect of Drainage on Temperature " 



Time 


Thermometer 

1 inch below 

surface 


Thermometer 

2 inches below 

surface 


Thermometer 

4 inches below 

surface 




Drained 


Undrained 


Drained 


Undrained 


Drained 


Undrained 


6 A.M 


48.0° F. 

82.5° F. 
71.0° F. 


49.0° F. 
70.0° F. 
63.0° F. 


48.0° F. 
80.0° F. 
73.0° F. 


49.0° F. 
69.0° F. 
65.0° F. 


49.5° F. 
75.0° F. 
74.5° F. 


49.0° F. 


Maximum 

6 P.M 


68.4° F. 
67 5° F 







removes the gravitational or free water, thus lowering the specific 
heat so that the same amount of heat applied will raise the tempera- 
ture more than if the soil contained much moisture. 



302 



SOIL PHYSICS AND MANAGEMENT 



It is very interesting to note the effect of drainage in the above 
experiment upon the germination of seeds and early growth of 
plants in the drained and undrained soil (Fig. 95). 

4. Presence of Water. — Aside from the lowering of tempera- 
ture by evaporation of water from soils, the presence of water keeps 
the temperature down because of the slowness with which it changes 
or because of its high specific heat. This is partly the cause of 
peats, clays, and undrained land being cold and late. If a cubic foot 
of dry soil having a specific heat of 0.3, weighing 100 pounds, should 
have 100 heat units applied to it, its temperature would be increased 
five degrees Fahrenheit. If a cubic foot should contain 20 pounds 
of water, its temperature would be increased two and one-half 
degrees, or the specific heat of the soil would be doubled. Sand 
soils are " early " because of the small amount of moisture which 
they contain and their low specific heat. 

5. Abscrption and Radiation o£ Heat. — The absorption of 
heat by soils and consequently their temperature depends largely 
upon their color. The dark colors absorb more heat than light ones. 
Black, blue, brown, and red absorb heat in the order given, while 
green, yellow, gray, and white absorb less, white being the slowest 
absorber of all. Bouyoucos colored white sand with dyes and deter- 
mined the comparative absorbing poAver as measured by the tempera- 
ture obtained. This table gives the results : 



Effect of Color on Temperature of Sands ^^ 





July 


27-28 


August 5-6 


Color of sand 


Maximum 


Minimum 


Maximum 


Minimum 




2 P.M. 


4 A.M. 


2:30 P.M. 


4:30 A.M. 


Black 


40.9 " C. 


16.7 ° C. 


37.6 ° C. 


12.45° C. 


Blue 


40.0 ° C. 


16.65° C. 


36.7 ° C. 


12.4 ° C. 


Red 


38.55° C. 


16.65° C. 


35.9 °C. 


12.4 ° C. 


Green 


37.10° C. 


16.60° C. 


34.7 ° C. 


12.3 ° C. 


Yellow 


35.8 ° C. 


16.60° C. 


32.65° C. 


12.25° C. 


White 


34.6 ° C. 


16.44° C. 


31.7 °C. 


12.2 ° C. 



A very interesting demonstration is to fill a tray three by six 
feet with soil, plant an equal number of seeds in each half of the 
tray, and cover one-half with very dark soil and the other half with 
white soil and place in the sunshine (Fig. 134). For best results 
this should be carried on in spring or fall. Plants come up from 24 



TEMPEEATURE 



303 



to 72 hours sooner in the part of the tray covered with dark soil. 
The table following gives the temperature in the two parts of 
the tray : 

Effect of Color on Soil Temperature " 



Time 


Thermometer bulb 
1 inch below 
surface 


Thermometer bulb 

2 inches below 

surface 


Thermometer bulb 

4 inches below 

surface 




Light 


Dark 


Light 


Dark 


Light 


Dark 


6 A.M 

Maximum 

6 P.M 


48.8° F. 

71.5° F. 
71 5° F 


50.0° F. 

82 °F. 
66 5° F 


47.5° F. 

70.8° F. 
74 5° F. 


49.0° F. 

78.5° F. 
70 ° F. 


48.5° F. 

78.4° F. 
77 °F. 


50.5° F. 

71.3° F. 
71 °F. 














Increase 


10.5° F. 


8.8° F. 


7.1° F. 




Fig. 134. — Difference in growth on light and dark colored soils. A, corn; B, wheat; C, water- 
melon. 

The time and the number of plants coming through the soil 
are governed to some extent by the color of the soil, as is shown in 
the following table. 



304 



SOIL PHYSICS AND MANAGEMENT 



Time Required and the Number of Plants that Came Up in the Soils of Different 
Colors. One Hundred Seeds Were Planted in Each '^ 





Wheat 


Oats 


Corn 


Melons 


Days after planting 


Light 


Dark 


Light 


Dark 


Light 


Dark 


Light 


Dark 


7 


's 

29 
51 
58 
62 
65 


4 

75 
86 
86 
86 
86 
86 


27 

70 
75 
75 

75 


6 

80 
100 
100 
100 
100 
100 


1 

66 

72 
72 


6 
84 

95 
95 
95 


'4 

32 
57 




8 




9 




10 


21 


11 


60 


12 


85 


13 


86 



With black the absorption is almost complete. The soils of what- 
ever color tend to cool to the temperature of the surrounding 
atmosphere during the night or in cloudy weather. The table on 
page 302 shows that the lowest temperatures of the dark-colored 
sands were not as low as the light-colored ones. Color has little 
influence in very wet soils since evaporation is a greater factor in 
lowering temperature than color is in raising it. 

6. Latitude or Angle of the Sun's Rays. — All flat areas of 
the earth's surface have the same number of hours of possible sun- 
shine annually without regard to location on the earth. The effect 



i/erficat 




Fig. 135. — Showing the comparative areas covered by the sun's rays when vertical, 30, 60, 
and 80 degrees from the vertical. Compare AB, AC, AD, and AE. 

of the rays in warming the soil depends upon the angle at which 
they strike (Fig. 135). If a sunbeam striking the earth's surface 
perpendicularly covers an area of 1, when this same beam strikes 
at an angle of 30 degrees from the vertical, it will cover an area of 
1.175 ; at 60 degrees it will cover an area of 2, and at 80 degrees 
an area of 6. The heat will be spread over a larger area the greater 
the distance from the vertical, and the effect on temperature would 
be inversely as the angle. The atmosphere absorbs some heat. The 



TEMPEEATURE 



305 



vertical ra3's pass through a thinner stratum of air than the other, 
and more heat will reach the surface from a vertical' sun. The 
effect of greater inclination is compensated for in summer to some 
extent bj the longer sunshine period in tTvent5^-four hours for high 
latitudes. 

7. Slope. — The slope of land has somewhat the same effect as 
latitude on the concentration and distribution of heat. The effect 
is to cause the ra3's from the sun to strike the south slope at a less 
and the north at a greater angle from the perpendicular (Fig. 136). 
With the sun 45 degrees above the horizon and the hill having the 
two slopes of 20 degrees of equal length, the south one would receive 
twice as much heat from the sun as the north one. 

"Wollny found that the average temperature of the south slope of 
a 15-degree hill was 1.5 degrees F. higher than the north slope. 




Fig 136. — Effect of slope on the area covered by the sun's rays. Angle of sun's rays 
30 degrees from vertical. EF is 100 per cent greater than DE. BC is 40 per cent greater 
than AB. 

King found that on Jul}^ 31 a south slope of 18 degrees had a tem- 
perature 3.1 degrees F. higlier than the level at a depth of one foot; 
2.7 degrees at two feet, and 2.8 degrees at three feet. For early 
crops a south slope is desirable. Plants that are liable to injury 
from spring frosts should be placed on north slopes so that growth 
will be retarded as much as possible. 
20 



306 



SOIL PHYSICS AND ^L\XAGEMEXT 



S. Conductivity of Soil Material and Soils. — Wet soils are 
better conductors of heat than dry ones and compact ones better 
than loose ones. These differences are due to the fact that air is a 
very poor conductor, even poorer than water. Soils should not con- 
duct heat downward very rapidly in spring, but should cause concen- 
tration of heat in the surface two to four inches to hasten germina- 
tion and aid the growth of the young plant. Of all soil materials 
quartz shows the highest rate of conductivity, while dry powdered 
chalk shows the lowest. 

In the following table it will be well to note the difference 
between loose and compast, wet and dry, and fine and coarse. 

Relative Conduciinty of Soil Material ^ 



?oil material 



Dry 


Loose 


Compact 


100.0 


106.7 


90.7 


90.7 


90.7 


96.4 


85.2 


92.6 


112.1 




115.6 




100.0 




103.6 




105.3 


moist 


100.0 


174 



Wet 



Quartz powder 

Peat. 

Kaolin 

Chalk 

Clay with limestone stones . 
Clay with quartz stones . . . 

Quartz sand, fine 

Quartz sand, medium 

Quartz sand, coarse 

Quartz sand 



201.7 

94.3 

155.6 

153.2 



1890 



The next table shows the length of time required after the air 
temperature had begun to rise for the heat to penetrate the soil to 
the depths given in the table. The conductivity of soils does not 
play a great part in practical agriculture except early in the spring 
when the greater conductivity of sand soils permits them to warm 
up earlier and to a greater depth, thus giving the crops grown upon 
them the advantage of several hours of warmer soils each day. 

Reltii'-'e Time for Heat to Penetrate the Soil Under Field Conditions ^* 



Date 



Depth 



Gravel 



?and 



Loam 



Clay 



Peat 



July 27.... 
August 5 . . 
August 26 . 

August 27 . 
September . 



inches 

6 
12 

6 
12 

6 
12 

6 
12 

6 
12 



hrs. tnCn. hrs. min. hrs. min. I hrs. min. I hrs. 



30 



30 



4 
7 
4 
7 
4 
7 
4 
6 
4 
I 5 



30 



6 

9 

6 

10 

7 
10 

6 
10 

6 
30 9 



30 
30 



6 
9 

I 5 
9 

6 
30 1 10 

5 
30 10 
30 6 

9 



30 
30 
30 



30 
30 



9 



30 



9 30 



TEMPERATURE 



307 



The following table gives the average soil temperatuie at varj-ing 
depths for ten years : 

Average Soil Temperature, 1905-1 9 14 10-Year Average in Bluegras'< Sod^^ 



Depth — Inches 



Jan. Feb. I Mar.j Apr. 



May 



June i July Aug. Sept. 



Oct. Nov. ! Dec. 



1. 

3. 

6. 

9. 
12. 
24. 
36. 



31.3 
31..5 
32.5 
33.2 
34.4 
39.4 
41.4 



30.9 
30.6 
31..5 
32.1 
32.7 
37.2 
38.8 



40.0 
39.6 
38.9 
38.3 
38.0 
38.0 
40.2 



.50.9 
50.7 
49.6 
49.2 
48.7 
47.2 
46.1 



62.8 
62.2 
60.4 
.59.8 

58.8 
.55.3 
.53.1 



72.71 76.7 76.4 68.6 
72.0 75.8! 75.8 68.2 
69.8 74.2] 74.0 68.2 



68.5 
68.2 
62.7 



73.51 
72.81 
68.3 



60.5 65.7 



73.3 67.9 
72.9 67.6 
69.5' 66.7 
67.5 65.9 



DO 

.54. 
.54. 
55. 
56 
.59. 
60. 



42.4 
42.8 
43.4 
44.3 
45.4 
49.9 
.52.1 



35.6 
34.9 
35.3 
36.2 

37.8 
43.5 

45.8 



It will be noted that the highest average temperature to a 
depth of nine inches is reached in July, while for greater depths the 
highest is reached in August. This is due to the slow conductivity 
of the soil. 

9. Tillage. — In general, tillage has two effects upon soils as 
regards temperature. It increases evaporation at first, but when the 
surface becomes (hry this layer acts as a mulch, preventing the moi.?t- 
ure from coming to the surface when the heat is used in evaporating 
it. Tillage loosens the soil, making it a poor conductor of heat. 
This concentrates the heat in the surface two or three inches of 
soil, and gives better conditions for germination early in the spring. 
Later in the season, when the unfilled soil has become somewhat 
dry, the conditions are reversed, and the tilled soil is cooler than the 
unfilled. 

QUESTIONS 

1. Why is a knowledge of the functions of heat and its control important? 

2. Illustrate the amount of heat received from the .sun. 

3. Why do high altitudes receive more heat from the sun than low ones? 

Why are high altitudes colder ? 

4. After the manure becomes thoroughly decomposed and mixed with the 

soil, what effect will it have on temperature? 

5. Why should water vapor raise the temperature of soil material more 

than liquid water? 

6. What effect does color have on radiation of heat? 

7. Why is conduction of heat downward into soil so slow ? 

8. Why is slow germination of seeds undesirable? 

9. Is the temperature of the soil usually at the optimum, as shown in the 

table on page 298, when the seeds are planted? 

10. What part does osmosis pilay in germination? 

11. How does temperature affect it? 

12. What effect does color of soil have on a cloudv dav? 

13. How does the specific heat of soils compare with other substances? 

(See tables, page 299.) 



30S SOIL PHYSICS .\ND MAXAGEMEXT 

14;. How does the specific. heat of hiuuus compare with other substances 
found in soils? 

15. What is the elfect of evaporation on tempera tute" of soils? " * 

16. Explain the elTeet of moisture on specific heat of soils. 

17. iTive the rigtires in r«rard to the elTeots of windbreaks. 

IS. How many heat units would be required to raise the temperature of a 
oxibic foot of soil live degrees if it weighs SO pounds, water-free, and 
contained 20 per cent of water? Specific heat of soil. 0.21. 

19. Give conclusion of experiments of Bouyoucos in table on page 302 with 

colored sands. 

20. Try the experiment with seeds planted in different colored soils. 

21. What effect did color have on different seeds? Why did melons show 

lower germination " 

22. What iutiuence does color have on very wet soils? 

23. Explain effect of latittide on temperature of soils, 

24. Explain action of atmosphere in al>sorption of heat. 

25. What is the effect of slope on temperature? 

26. What part does conductivity play in temperature? 

27. Which will warm up quicker in spring, a cultivated soil or a compact 

soil? Why? 

28. WTiy is dry, loose chalk a poorer conductor of heat than quartz powder ? 

29. Why is fine sand a poorer conductor than coarse sand? 

30. Why is wet soil a better conductor than dry? 

31. For truck crops do we need good or poor conductors ? 

REFERENCES 

^GJeorgeson. Agriculttiral Science I. p. "251. 

=* Stellwaag. Wollny, Forsch. der Agricultur Physik. Vol. 5. p. 210. 

'Bouyoucos, George -J., Technical Bulletin 17. Michigan Station. 1013. An 

Investigation of Soil Temperature and Some of the Most Important 

Factors Infiuencing It. p. 30. 
*rioth. Flora. 1S71. p.'"lS5. 

* Haberlandt. F. Landw. Versuchs-Stationen. x\ii. p. 104. 
*Hall. A. D.. The Soil. 1912. p. 123. 

'Duff. A. Wilmer. A TextKiok of Physics. 1912. p. 232. 
^Bouvoucos. G. J.. I see above), p. 12. 

* Patten. H. E. Bulletin 59. Bureau of Soils, U. S. D. A.. Heat Transference in 

Soils- 1009. p. 34. 
^* Patten, H. E.. (see above), p. 27. 
" Unpublished Data, University of Illinois. 
"Bouyoucos. G. J., (see above), p. 31. 
° Pott. H. E.. Landw. Versuchs-Stationen, xx, p. 2SS. 
"Bouvoucos, G. J., (see above), p. 19. 



CHAPTEE XXIV 

SOIL AIR AND AERATION 

Evert individual who has grown crops knows that a soil must 
contain air as well as water, and the amount of one will vary with 
that of the other. In other words, the air of a soil occupies that 
space not occupied by water, and when the proportion of the two 
is about equal optimum conditions prevail. 

-Use of Air in Soils. — ^The most important element in soil 
air is oxygen. It is necessary for the vital functions that take 
■place in plants, and in the case of water-logged soils, in which the 
oxygen is reduced to a minimum, the effect can readily be seen. 
Oxygen is necessary for root respiration. We find that there is an 
interchange in the roots, the carbon dioxide being given off and the 
oxygen taken in. Oxidation, with or without the agency of bacteria, 
is necessary for furnishing available plant food for the crop. The 
process that supplies available nitrates is known as nitrification, and 
takes place through the agency of organisms. This is absolutely 
necessary in soils, and if for any reason oxygen is prevented from 
entering the soil, or if the supply becomes low, the lack of nitrates 
is shown by the yellowish-green color that the plant soon assumes. 

A-supply of oxygen is necessary in the soil for germination also. 
Certain chemical processes take place in the seed for which oxygen 
is necessary. 'In extremely wet soils seeds germinate very poorly. 
Air is necessary in the soil for supplying nitrogen to the nitrogen- 
fixing bacteria, both symbiotic and non-symbiotic. The carbon 
dioxide of the soil air is of importance because of its effect on min- 
erals. These are slowly decomposed by the carbonic acid that is 
formed, and plant food is liberated. 

Amount of Air in Soils. — The amount of air in soil depends 
upon the porosity, and this upon the texture. It would naturally 
be" supposed' that the greatest amount of air would be in the soil 
having the highest porosity. This may not always be true, since 
soils with high porosity have also a high retentive capacity for 
moisture, and it would not be an unusual thing for a soil to retain 
so much water that it would reduce the actual amount of air present 
to a point less than that held b}^ sand, (See the table on composi- 
tion of soil air, page 310.) - 

309 



310 



SOIL PHYSICS AND MANAGEMENT 



The stnietuTe of the swl plays some part in the amount of air. 
This is especially true of fine-grained soils. If granulation exists 
the space bettreen tht granules will be largely occupied by air. even 
when the soil is well supplied with water. This may increase the 
amount of air so that it will compare very favorably with that in 
sand. The amoimt of organic matter present induences both the 
water retained and the porosity, but as a general rule it wUi in- 
crease the amount of air in soils, since it also increases the granu- 
lation. The most important factor in determining the amount of 
air in soil is moisture, which varies from week to week. After a 
heavy rain air may occupy only a small fraction of the total pore 
space. With the removal of the water by percolation, evaporation, 
and by rwts the aiiuniut of air increases. 

Composition of Soil Air. — ^W'hile the soil air contains sub- 
stances that are not found to any extent in the air above, yet in 
general the same elements and constituents are found in it as in the 
atmosphere. Thus we find the atmosphere composed of oxygen, 
nitrogen, and c-arbon dioxide, with a few other elements or com- 
pounds. In the soil air we find the same elements present, but not 
in the same prc^rtion. The carbon dioxide is much more abundant 

ComptmtioH of Soil Air as IMfrmined by BoitssmgamU and Ltwy ^ 



Ckuaetet of soil 



Voluiae in one acie 
of soil to dei>Ut of 
14 inehes 



Air 
(ett. ft- 



Carbon 

dioxide 



Composition of 100 parts of soil 
air by votume 



S^? <>-y*-- ^~**«««- 



Sandy subsoil of forest . 
Loamy subsoil erf forest. . . 

Stirface soil of forest 

CJay soil 

Soil of asparagus bed not 

raanured for one j-ear. . 
Soil of asparagus be<i 

freshly manured 

Sandy soil, six da\-s after 

manuring 

Sandy soil, ten days after 

nianuring \.three days of 

rain'! 

Vegetable mold compost. . 



4.416 
3,530 

10^310 

11,1^ 
11,182 
11,753 



11,783 
21.049 



14 

57 
71 

S6 

172 

257 



1,144 
772 



o.:4 

0.79 
0.S7 
0.66 

0.74 

1.54 

•2.21 



9.74 

3.64 



li'.oo 
19.61 
19.99 

19.02 

laso 



, v.. -■.-I 
79.52 
79.35 

sa24 

79.66 



10.35 

16.45 



79.91 

79.91 



Per cent by volume 



Orvi:",l^^" 



OS 



•"•O OS 



79. W 



SOIL Alli AND AERATIOX 311 

in soil air thun in the atmosphere, while the oxygen varies inversely 
wit}) the amount of carhon dioxide, the nitrogen remaining prac- 
tically the same. 

The ahove tahle shows the amount of carhon dioxide in soils 
under different conditions with the comparative amount of oxygen. 

Aeration or Soil Ventilation. — Aeration as spoken of in con- 
nection with soils is an interchange hetween the atmosphere and 
the soil air. It is necessary, first, to supply the oxygen needed hy 
roots and soil organisms; second, the supply the nitrogen needed by 
nitrogen-fixing bacteria, and, third, to remove the carbon dioxide, 
an excess of which becomes injurious because of the fact that it 
excludes oxygen. Soil ventilation may be accomplished in a variety 
of ways. 

(a) Diffusion is the mixing of gases of different compo.sition 
due to molecular movement. It may be well illustrated by filling 
a bottle with carbon dioxide, and although this gas is heavier than 
ordinary air, yet if the bottle is left unstoppered for a short time 
it will gradually diffuse into the surrounding atmosphere. As seen 
in the preceding table, soil air contains a larger amount of carlxjn 
dioxide than the atmosphere and it is constantly, but slowly, being 
removed by diff'u.-ion. This process takes place more rapidly in 
soils of large total pore space than in those with large individual 
pores, so that for heavier soils with a high porosity and a high air 
content, diffusion will take place more rapidly than in sandy soils 
with larger pores and a smaller total pore space. This seems con- 
trary to the fact that sandy soils are better aerated than clay soils, 
hut it must be remembered that other agencies are at work that 
bring about better aeration in sandy soils. Compacting a soil, by 
any means, tends to lessen diffusion because it lessens the total 
pore space. For this reason a soil in good tilth permits more rapid 
diffusion than one in poor tilth. Temperature affects diffusion in 
that a higher temperature produces greater molecular activity, 
which results in more rapid interchange of the gases. 

(b) Removal of Water. — The removal of water from the soil 
by any process permits air to enter, thus bringing into the soil a 
new supply of pure air. As the water is carried out by drainage 
the air follows downward from the surface. The removal of water 
by the roots of plants has the same effect, but the change is very 
slow. 

(c) Changes in Atmospheric Pressure. — Barometric pressure 
is not constant. Eegular changes take place in the region of the 



312 



SOIL PHYSICS AND MANAGEMENT 



prevailing westerlies every three or four days, corresponding to the 
movement of " highs " and ^' lows." These variations amount to 
an average of about one-half inch in the height of the mercury. At 
the Illinois Station the average weekly' change for five years has 
been 0.45 inch. The minimum during this time was 0.20 inch, 
while the maximum was 1.45 inches. According to Boyle's law, a de- 
crease in pressure increases the volume of a gas, while an increase in 
pressure diminishes it and in proportion to the increase or decrease. 
A difference of 0.5 inch in pressure is equivalent to 1/CO of an 
atmosphere. If a cubic foot of soil with 50 per cent of pore space 
has one-half of this occupied by air, it will contain 433 cubic inches 
of air. An increase in pressure of 1/60 of an atmosphere will 
force seven cubic inches of air into the soil. With a corresponding 
decrease in pressure the soil air expands, forcing out the same 
amount. 

(d) Temperature Changes. — When gases are heated they ex- 
pand, and when cooled they contract. The amount of expansion or 
contraction is a definite qu-antitv\ Air changes in volume 1/491 
for each change of one degree Fahrenheit, or, 1/273 for each degree 
Centigrade. If a cubic foot of soil contains 432 cubic inches of 
air, a change of one degree will result in a change of approximately 
one cubic inch in volume. During the growing season the average 
daily range for soils to a depth of four inches is about twelve degrees, 
as shown in the table below. 

Range of Temperature of Plowed and Unplowed Land at Different Depths 
{Degrees Fahrenheit) — Average 1912-1915 - 



Depth 


Two inches deep 


Four inches deep 


Treatment 


Plowed 


Not plowed 


Plowed Not Dlowed 






*^ 


May* 

June 

July 

August 


12.8 
13.6 
16.0 
14.1 


11.2 
13.8 
17.7 
13.6 


10.3 
13.1 
13.2 
11. .5 


9.8 
15.7 
15.6 
11.1 



* Average of 2 years. 



This would give a change in volume of about 12 cubic inches in 
a cubic foot of soil, and this amount would be expelled during the 
day and taken in at night. The aeration brought about by changes 
in pressure and temperature produces almost a complete change of 
the air in the surface few inches of soil each week. 



SOIL AIR AND AERATION 313 

(e) Tillage is the most effective method for producing a change 
of soil air. The best implement for accomplishing this purpose is 
the plow. When the furrow slice is turned over the shearing pro- 
duced pulverizes the soil and brings about a. complete change of air 
in all except the granules, and breaking the soil up brings about a 
much better chance for a change in these. Any form of tillage, 
however, will materially aid aeration. Plowing cloddy ground ac- 
complishes the least. When these clods are thoroughly pulverized 
much better interchange takes place, and this is one of the great 
advantages of thorough pulverization of the soil. 

(f) Wind Movement. — The wind as a general rule moves in 
gusts, and these passing -over a field have a tendency to draw out 
the air from the soil and aid aeration to some extent in this way. 
Any exact determination of this effect of wind would be very diffi- 
cult, yet it is probable that on soils having large air spaces, such 
as cloddy or sandy ones, this plays quite an important part in 
aeration. 

Water-logged Soil. — ^Lanj soils which have imperfect drain- 
age due to a high water table or an impervious stratum may con- 
tain such a large amount of water as to exclude the air, resulting 
in a very serious condition, so far as the vital soil activities are con- 
cerned. The remedy, of course, is drainage, and the drainage 
should be sufficiently complete so that a heavy rainfall will not 
saturate the soil for any length of time. If the water table is two 
or three feet from the surface, a heavy, rain may raise this sufficiently 
to injure the crop unless the soil is 'thoroughly drained. Many 
systems of drainage have not been sufficient to lower the water table 
rapidly and the result is that in wet -seasons the crop is badly 
damaged. Even in moderately wet seasons the crop in the lower 
places where the water table is near the surface will assume a 
yellovrish-green color, indicating that injury is being done by lack 
of aeration. ' ■ • 

Running Together. — Soils that are deficient in organic matter 
are in condition to be easily puddled, especially the fine and medium 
grained ones. A heavy rain may be sufficient to do this. The 
beating of the rain drops breaks the granules into individual par- 
ticles that render the surface impervious both to air and water, thus 
cutting off the supply of air. If this condition continues for any 
length of time, the crop may be retarded in its growth and be- 
come of a greenish-yellow color, indicating nitrogen starvation. 
The remedy, of course, is tillage for breaking the crust and aerating 



314 SOIL PHYSICS AND MANAGEMENT 

the soil. If a heavy soil ox a soil rich in organic matter should 
become puddled in this way by a shower, upon drying, shrinkage 
cracks will be formed through which air may enter. Tillage would 
not be so necessary in that case. In light sandy soils this puddling 
will not take place. 

QUESTIONS 

1. Give uses of air in soils. 

2. What are some indications by the plant that oxygen is deficient? 

3. Upon what does the amount of air that the soil will contain depend? 

4. What causes variations in the composition of soil air? 

5. In table on page 310 what is the average amount of nitrogen? 

6. How does this compare with the normal amount in air? 

7. Define aeration. 

8. Why is it necessary? 

9. What is aiffusion? Illustrate. 

10. What effect does porosity have on diffusion? 

11. How does temperature affect it? 

12. How does removal of water aid diffusion? 

13. How much change in atmospheric pressure in a week? 

14. What is Boyle's law? 

15. What part of an atmosphere is represented by a change of 0.45 inch 

of pressure? 

16. How does atmospheric change effect aeration? 

17. Explain the effect of temperature changes on aeration? 

18. Give average change for the four months for each depth and for each 

treatment. 
IP. How much of a change in volume would occur for each if the soil 
volume were one-fourth air ? 

20. Explain the effect of tillage on aeration. 

21. Give effect of wind movement. 

22. What is a water-logged soil ? 

23. How may it be avoided? 

24. Why is it detrimental to the crop ? 

25. What effect does running together have on aeration ? 

REFERENCES 

^Johnson. S. W., How Crops Feed, 1891. p. 219. 
^ Unpublished Data, University of Illinois. 



CHAPTEE XXy 

SOIL ORGANISMS 

The soil contains large numbers of organisms, both plants and 
animals of various kinds, that act upon both the organic and min- 
eral constituents of the soil. They produce changes, many of which 
are highly beneficial, while others are detrimental. For convenience 
they may be divided into macro-organisms, such as rodents and m- 
sects, and micro-organisms, those of microscoj)ic size, such as fungi 
and bacteria. 

MACEO-OKGAi^ISMS 

1. Rodents. — Large numbers of rodents, such as squirrels, rats, 
mice, prairie dogs and gophers, have, the habit of burrowing in the 
soil, thus facilitating the action of certain agencies. These carry 
soil upward and a more thorough mixing of the surface and sub- 
soil is thus brought about. Later these openings are filled with 
surface soil. Much vegetable matter also is carried into these 
burrows, which helps in decomposition of the minerals with which 
it comes in contact. Aeration and percolation are aided by the work 
of these animals. It is interesting to note that very few burrowing 
rodents are found in regions of tight clay subsoils. 

2. Insects. — A great many insects live in the earth during their 
larval state or even the whole of their lives. The larval stage of in- 
sects is their most active period. They are constantly working 
their way through the soil and in this way aid aeration and drainage. 
Seventeen-year locusts are very abundant in soils in some local 
areas. Over 500 exuvias, or cast-off shells, of these insects were 
counted upon a hawthorn bush not over three feet high. Ants 
work up their hills, filling them with vegetable matter, and when 
they are abandoned form very rich spots of soil. 

3. Worms. — Earthworms are most common organisms and 
are- found in medium and heavy soils of humid areas that are well 
supplied with organic matter. They do not seem to be so abundant 
in acid soils, evidently preferring those containing some limestone. 
They do not live in sands, light sandy loams, arid or semi-arid 
soils. They aid in aeration and their burrows improve drainage. 
They pass large quantities of soil through their bodies. The min- 

315 



31G SOIL PHYSICS AND xMAXAGEMENT 

erals are acted upon by the acids of the alimeutary canal, produciug 
chemical chauges resultiug in the liberation of plant food. They 
carry large amounts of, soil, from, the subsurface and subsoil and 
deposit it on the surface of the ground, where it may be seen as 
casts, especially in the morning after a rain. Darwin states that 
where earthworms abound the amount brought by them forms a 
layer from 0.1 to 0.2 inch in thickness each year. This amounts to 
from 15 to 30 tons per acre. Some comparative experiments have 
.been conducted which show that earthworms increase the yield of 
crops. 

- : 4. Plants. — The soil is modified to a large extent by the roots 
of all plants, whether large or small. The short-lived annuals and 
biennials have the greater effect, because new roots are formed every 
one or two years. The roots of perennial prairie grasses are great 
factors in modifying soil because of their great abundance . and 
■deep penetration. While most of the roots of trees and shrub's live 
for years, yet many die every season. Eoots of all plants add some 
organic matter to the soil, but they have another important effect. 
They make the soil more porous after they decay and. thus improve 
aeration and drainage. Frequently when timber spreads over a 
prairie area having a tight clay subsoil the ultimate effect of the 
roots is to lessen the impervious character of the subsoil so that 
drainage takes place with much less difficulty. 

Many fungi live on and in the soil and affect it to some extent. 
Some aid in the early decomposition of vegetable matter. Others 
are diseases, such as some smut and scab. Others live in sym- 
biotic relation to certain higher plants. These through the agency 
of large numbers of hyphte or fungi rootlets, called michoriza. trans- 
fer the food to the companion plant. 

illCEO-OEGAXISilS 

The group of micro-organisms, consisting of bacteria, fungi. 
protozoa, a.\gse and yeasts, is of special importance in soils. They 
aid in the transformation of the vegetable and animal remains into 
the humus-like residue, which really constitutes part of the soil. 
They carry on many other operations- that benefit soils chemically 
and to some extent physically. However, the physical condition of 
soils and the phenomena that occur in them which influence the 
work and development of these micro-oro-anisms are so important 
that they merit considerable attention. How the farmer mav in- 



SOIL ORGANISMS . , ^17 

■fluence the work of these organisms is a question that every one 
interested in agriculture should know. The micro-organisms m the 
soil are of two general kinds, injurious and beneficial. 

1. Injurious Organisms. — After a soil has been cropped for a 
number of years it is frequently found to contain numbers of or- 
ganisms of various -kinds, some of which are not only of no benefit 
to the crop, but are actually injurious. The number and' char- 
acter of these depend largely upon the crops grown and the rota- 
tion practiced. A single crop system is likely to encourage the de- 
veloiDment of organisms injurious to that crop. Hence a rotation is 
advisable. 

Some of these are the wilt of cotton, flax, cowpeas, probably 
clover .sickness, the scab of potatoes, the rots of many plants. These 
perish when by rotation they are deprived of their host plants for 
a few years. 

2. Beneficial Organisms. — The beneficial organisms comprise 
a considerable number of forms, but the group of bacteria is of 
special importance. It would be impossible to grow crops with- 
out these. They are the farmer's best friends." They aid him in 
getting plant food into the soil in the process of nitrogen fixation 
and are of vital importance in making plant food available, as in 
the process of nitrification. 

(a) Fixation of Nitrogen. — Some bacteria in the soil live in 
symbiotic relation with legumes, producing nodules or tubercles upon 
the roots. Their function as they grow in this connection is to take 
nitrogen from the soil air and put it into the plant, in this way 
storing up or fixing nitrogen. These organisms live in this relation- 
ship with legumes and this explains the importance of this class of 
•plants to the farmer. Turning under the legumes enables the 
farmer to get a supply of nitrogen into the soil with little expense 
and in a form that is readily available to other plants which can 
use only soil nitrogen. In general each legume has its own 
special bacteria. 

Aiiother class of bacteria known as Azotobacter have the power 
of fixing nitrogen in the soil directly or independent of any other 
plant. To what extent this is done is not definitely known, but no 
doubt it is of sufficient consequence to justify careful consideration 
in producing favorable conditions for their activity. 

(b) Nitrification. — The nitrogen of soil organic matter cannot 
be used directly by our crops. It must first be changed into some 
readily soluble form, usually nitrates. Some crops, such as rice and 



318 SOIL PHYSICS AND MANAGEMENT 

potatoes and possibly others, may use more or less of it in the form 
of ammonium compounds. By far the larger part is taken up by 
plants as nitrates. The soil nitrogen must be changed to this form. 
The process of nitrification is the changing of the nitrogen of soil 
organic matter into nitrates, and is accomplished through the ac- 
tion of certain classes of bacteria. The steps in the process are as 
follows : 

(1) Ammonhfication, in which the organic matter is decom- 
posed by bacteria and the nitrogen changed into ammonia or com- 
pounds of ammonia. 

(3) Nitrification proper, which consists of the formation of 
nitrous acid or nitrites from the ammonia or ammonium com- 
pounds and the subsequent change to nitric acid or nitrates. This 
is essentially oxidation. The nitrous and nitric acids unite with a 
base of the soil. As calcium is one of the most common and readily 
available bases, calcium nitrate is usually formed. 

DISTRIBUTION" AXD COXDITIOXS 

1. Distribution. — The bacteria concerned in nitrification are 
very widely distributed in all kinds of soil, with the possible excep- 
tion of swamp or long flooded soils. They are much more abundant 
in soils containing limestone than in strongly acid ones. The sym- 
biotic bacteria for legumes are found practically everywhere, but 
not the specific forms for all legumes. The bacteria for alfalfa are 
very widely distributed over western regions of the United States, 
but in the eastern region inoculation, which is the process of sup- 
plying the proper bacteria, is necessary. The same is true of many 
other legumes. Wild legumes sometimes carry the same bacteria 
as our cultivated ones. 

The number of bacteria changes with the type of soil. On the 
same kind of eoil the number of bacteria varies with the degree of 
fertility, the tilth, and the rotation practiced. 

In vertical distribution the bacteria increase in number from 
the surface downward for four to six inches and then decrease rap- 
idly with depth and are found several feet below the surface only 
as they are carried downward by percolating water. The zone of 
greatest number of bacteria is from five to six inches beneath the 
surface, but it will vary somewhat with the soil tvpe, being a little 
deeper in well-aerated soils. The optimum conditions of tempera- 
ture, moisture and aeration are found at this depth. The following 



SOIL ORGANISMS 



319 



table gives the number of bacteria at various depths under different 
systems of cropping at the Iowa Station : 

Bacteria per Gram of Air-Dry Soil ^ — Rotations 









Corn, oats, 




Depth of sampling 


Continuous corn 


Corn, corn, oats, 
and clover 


clover turned 

under first 

season 


Corn, oats, 
clover 


4 inches 


1,752,000 


2,912,000 


4,148,250 


4,164,000 


8 inches 


1,248,250 


2,027,000 


3,591,000 


2,943,750 


12 inches 


546,000 


560,500 


1,167,750 


907,500 


16 inches 


298,250 


316,000 


348,250 


315,000 


20 inches 


153,500 


256,000 


223,000 


155,750 


24 inches 


93,850 


89,225 


108,750 


91,825 


30 inches 


48,500 


49,025 


60,125 


53,775 


36 inches 


31,600 


32,475 


37,625 


34,800 



It will be noted that the number of bacteria at four inches in 
depth is greatest in the rotation which brings the clover crop on 
the land more frequently. The difference is very striking when 
compared with continuous corn. 

The Kansas Station found that the number varied directly with 
the fertility of the soil. 

2. Conditions for Development. — It is generally known that 
most plants require very favorable conditions for their growth, such 
as food, moisture, heat, air, light, and the physical condition of the 
soil. The same conditions that are favorable to higher plants are 
favorable for the activity of bacteria, with the exception of light. 

.(a) Moisture. — Bacterial activity . involving chemical change 
ceases in dry soil. The other extreme, a water-logged soil, is almost 
equally inhibitive of the action of bacteria. When a soil has ap- 
proximately half of its air space filled with moisture the conditions 
are most favorable for bacterial activity and their growth is most 
rapid. 

(b) Food, — Organic matter is a very important food for most 
bacteria, but some of the beneficial organisms obtain their supply 
of carbon from carbon dioxide. They develop in great numbers in 
drained soils having an abundance of organic matter. Small 
amounts of mineral food are required, but soils usually contain 
sufficient quantities for the use of these organisms. Soluble organic 
matter in considerable quantities tends to inhibit nitrification. ISTor- 
mal soils contain very little. Large amounts of sewage are not de- 
sirable on land because it furnishes soluble organic matter. 



320 SOIL PHYSICS AND MANAGEMENT 

(c) Temperature. — ^Tlie optimum temperature for bacterial 
activity lies between 65 and 95 degrees F. (18 and 35 degrees C). 
It diminishes as the temperature increases, and at 130 to 11:0 degrees 
F. action ceases and many are killed. Below 65 degrees F. the bac- 
teria become less active and cease at 32 degrees F., although they 
are not killed. Early tillage, drainage and a dark color raise tem- 
perature and encourage bacterial action. 

(d) Aeration. — Bacteria' are divided "into two general classes, 
aerobic, those requiring oxygen for their growth and activity or 
work, and the anaerobic, which require no oxygen. Aeration is very 
essential to the first group. Since nitrification is the most im- 
portant work of bacteria in soils the amount of nitrates produced 
may be taken as a measure of their activity. Experiments show 
that in the absence of oxygen not only were no nitrates formed, but 
the nitrates present were reduced with evolution of free nitrogen. 
AVhen six per cent of oxjj'gen was present the amount of nitrates 
formed was double what it was with 1.5 per cent.- 

(e) Reaction. — Soils giving acid reactions are not very favor- 
able to the work of bacteria. They are more active in soils that 
are neutral or slightly alkaline. The nitrifying bacteria produce 
nitrous and nitric acids, which tend to inhibit their action. If 
bases are present in the soil these will unite with the acids pro- 
duced, thus keeping the soil neutral or alkaline, and in good con- 
dition for their work. Limestone should be applied to the soil to 
neutralize the acidity. 

Crops growing on water-logged soils are usually yellow. This 
is due to a lack of available nitrates. The water excludes the air 
and the bacteria cannot do their work. The same conditions exist 
when a soil in poor tilth runs together and liakes, forming a crust 
impervious to air. When aeration is produced by cultivation 
nitrates are formed and a crop such as corn resumes its normal dark 
green color. 

' Another important function of aeration is to remove the carbon 
dioxide of the soil air. This is necessary because it excludes oxygen. 
In the process of nitrification carbon- dioxide is formed. Tillage is 
the best means of bringing about aeration. Deherain ^ conducted an 
experiment which shows the effect of tillage on aeration and con- 
sequently upon the action of nitrifying bacteria. A quantity of 
soil was thrown upon the floor and worked daily for six weeks. At 
the end of this time the stirred soil contained 23.7 times as much 
nitric nitrogen as the soil not disturbed. " JSTitrate farming " as 



SOIL ORGANISMS 



321 



formerly practiced is an application of this principle. The soil rich 
in organic matter was stirred and moistened to develop a large 
amount of nitrates, which were then leached out and used for com- 
mercial purposes, principally in the manufacture of gunpowder. 

Effect of Different Amounts of Lime Upon the Number of Bacteria per Gram 

of Dry Soil * 



Treatment 


Number of 
bacteria at 
beginning of 
experiment 


Number of 
bacteria after 

7 weeks 




504,000 
718,000 
657,000 
480,000 


417,000 


1000 pounds lime per acre 

2000 pounds lime per acre 


1,551,000 
1,322,000 
5.571,000 


4000 pounds lime per acre 



This table shows the effect of lime carbonate upon the number 
of bacteria and indicates a much greater development for the higher 
lime content. An excess of lime is not injurious, as in the case 
of some other alkaline carbonates as shown in the next table. 



Effect of Alkaline Carbonate Upon Amount of Nitrates Produced ^- 
LOOO Grams of Acid Soil 



Treatment 


Nitrates formed 


None 

1 gram K2CO3 

2 gram K2CO3 

3 gram K2CO3 

4 gram K2CO3 

5 gram K2CO3 


70 milligrams 
160 milligrams 
230 milligrams 
250 milligrams 
130 milligrams 

73 milligrams 



(f ) Physical Composition. — Certain j^hysical phenomena upon 
which bacteria depend for their greatest activity and development 
take place better in the medium-grained soils than in very fine ones. 
Very sandy soils are well aerated, but usually do not contain suf- 
ficient moisture and food. Granulation overcomes this in the 
heavier soils to some extent. Even with this aid aeration and the 
moisture conditions are not so favorable and nitrification is usually 
slower. Tillage is more essential for these soils. Where limestone 
is absent heavy soils may be unfavorable for bacterial activity. 
Limestone aids in granulation and thus indirectly in aeration. 

(g) Light. — Direct sunlight greatly weakens or even kills bac- 
teria. The zone of greatest numbers is sufficiently deep so that 

21 



'^oo 



SOIL PHYSICS AND MANAGEMENT 



sunlight does not ponotraro to it. All inoculating material and 
inoculated seed should be kept from direct sunlight, because of its 
drying effect. 

Loss of Nitrates. — Soils lose nitrates in three Avays: by leach- 
ing, denitritication and by the growth of weeds or other plants 
foreign to the crop. , 

1. Leaching. — The greatest loss of nitrates is through leach- 
ing. ]N"itrates are very readily soluble in water. During rains those 
formed in manure heaps or soil may be carried into drainage sys- 
tems and lost. That this does occur to a considerable extent is 
shown by analysis of drainage waters. 

Deherain collected drainage waters from cement tanks with 
results as given in the following table. The tanks had been filled 
several vears before. 



Ltwc? of Xitrates by Leaching ' 



Cropping 



Nitrogen as nitric 



Fallow, no cultivation 

Rve srass 

Oats 

Maize 

Wheat followed bv vetches. 

Wheat ■ 

Fallow, hoed 

Fallow, no cultivation 

Fallow, hoed and rolled 

Vine 

Sucar beet 



Drainage, inches 


nitrogen, pounas 
per acre in 




dnvinitge 


11.2 


1S6.7 


7.S 


2.2S 








4 .Ol 


6.9 


21.60 


6.6 


12.60 


7.5 


2S.70 


11.5 


196.56 


11.2 


loS.OO 


11.2 


1S3.20 


7.5 


36.20 


7 "^ 


0.27 



The rainfall during the season was CS.S inches. It is very inter- 
esting to note the effect of the crop on the amount of drainage and 
also on the nitrogen removed with the water. Catch crops are of 
value in preventing loss of nitrogen in this way. Even weeds may 
serve as a catch crop after the main crop is removed. 

Fallowing (leaving land without a crop and cultivating during 
summer') in humid areas is a very expensive operation and should 
never be practiced. It will not be necessary if the organic matter is 
properly maintained. Fallowing is resorted to when the active 
organic matter has been largely removed by cropping and some 
special means must be taken to render the less active form avail- 
able. This is accompanied with too mtich loss of the most expen- 
sive plant food, nitrates in soils, to be profitable. In the above table 



SOIL ORGANISMS 323 

the loss of nitrates by leaching from fallowed land is 181.1 pounds 
per acre, while the cropped land shows an average loss of 15.6 
pounds, or only one-tenth the amount of the fallowed. 

2. Denitrification. — Nitrification is an oxidation process, while 
denitriiication is one of reduction or deoxidation by which nitrates 
are broken down and free nitrogen given off. In other cases the 
change may be such as to form nitrites or ammonia. In the latter 
the nitrogen may not be lost from the soil by it. It takes place in 
soils when poor aeration results in a deficiency of oxygen, as in 
heavy, compact, puddled, or water-logged soils. Manure contains 
large numbers of denitrifying bacteria and extremely heavy appli- 
cations of coarse manure may result in some loss through the action 
of these organisms. 

QUESTIONS 

1. Wliat kinds of organisms are found in the soil? 

2. What are macro-organisms? Micro-organisms? 

3. Give the effects of rodents on the soil. 

4. Give the work of insects in soils. 

5. \Miere are worms most abundant? 

0. What work do they perform in soils? 

7. Give Darwin's statements of the amount of material brought to the 

surface. 

8. Give the effects of plants on soils. 

9. What is the work of micro-organisms in soils? 

10. What part do fungi play? 

11. Tell about the injurious forms. 

12. Give the two methods of fixation of nitrogen. 

13. What is nitrification? 

14. Tell about the steps in the process. 

15. Where are soil bacteria most abundant? 

16. What about the distribution of bacteria? 

17. How do the number of bacteria vary? 

18. How are they distributed vertically? 

19. What effect do different systems of cropping have? 

20. What two general classes of bacteria? 

21. Give the characteristics of each. 

22. Of what use is aeration to bacteria? 

23. Give the experiment by Hall. 

24. What was " nitre farming " ? 

25. Why should bacterial activity almost cease in soils of extreme moisture 

content? 

26. What temperatures are best for the work of bacteria? What are 

detrimental ? 

27. What are the foods of bacteria? i- -a , 

28. What part does the reaction of the soil play in bacterial activity? 

29. What conclusion do vou reach from tables on page 321? , . • i 

30. Why should the physical composition of the soil affect bacterial 

activity ? 

31. Give the effect of sunlight on bacteria. 

32. How are nitrates lost from soils? 



324 SOIL PHYSICS AND MANAGEMENT 

33. Give conclusions from table on page 322. 
oi. What eti'ect did cropping have on drainage? 

35. What is fallowing? 

36. Why should there be such a large loss of nitrates from the fallowed 

land? 

37. What is denitrification ? 

38. Under what conditions does it occur? 

REFERENCES 

'Brown, P. E.. Eesearch Bulletin 8, Iowa Station, Bacteria at Different 
Depths in Some Typical Iowa Soils, p. 2841. 

- Schlosina:, Compt. Bend. Aeademv of Science, Paris, vol. Ixxvii, pp. 
203-253. 

^ Deherain, Compt. Bend. Aeademv of Science, Paris, vol. cvi, 1893, pp. 
1091-97. 

^ Chester, Frederick E., Bulletin 98, Department of Agriculture, Penn- 
sylvania, 1902, p. 25. 

'Dumont, Compt. Bend. Aeademv of Science, Paris, vol. cxxv, 1897, pp. 
4()9-72. 

"Deherain, Noted by Hall, A. D., The Soil, 1912, p. 228. 



CHAPTER XXVI 

TILLAGE 

In the time of Jethro Tull (16T4:-1T41) the present theory of 
plant nutrition had not been advanced, and this well-known hus- 
bandman frequently made the statement that "tillage is manure." 
Wliile his theory was wrong, yet his practice was right. He believed 
that the object of fining the soil was to enable the plant to take up 
the small particles for growth. The practice resulting from this 
belief was as good as would have been brought about had the real 
theory of plant nutrition been known. We know now that the pur- 
pose of tillage is not to furnish fine particles of soil for the plant. 
However, tillage accomplishes a number of objects, many of which 
are closely related to the production of plant food for the crop. 

Tillage is the practice of working the soil for the purpose of 
bringing about more favorable conditions for germination and plant 
growth. All operations that affect the soil by stirring, inverting, 
fining, or firming are included in tillage. The most common are 
plowing, harrowing, rolling, and cultivating. 

THE OBJECTS OF TILLAGE 

1. Pulverizing and Loosening the Soil. — The. natural ten- 
dency of soils is to become compact, principally through the action 
of rain, and in spite of the influence of the roots of plants and the 
organisms in the soil whose tendency is to keep the soil loose and in 
good tilth. It is necessary, then, to stir the soil to allow the funda- 
mental processes that are vital to crops to take place. On the brown 
silt loam of the corn belt a rotation of corn, corn, oats, and clover 
was practiced. The soil was plowed preceding the oat crop and at 
no other time. The two crops of corn were planted in the unplowed 
soil, and a yield of 35.2 bushels per acre was produced as a nine- 
year average. The plowed land produced 13.7 bushels niore.^ 

2. Turning under vegetable matter and incorporating it and 
other fertilizers with the soil. In our farm practice it is necessary 
to maintain the supply of organic matter, and this can be done only 
by incorporating large quantities of vegetable material in the soil. 
When plants die and fall to the surface of the ground, unless some 

325 



o2c^ SOIL ruYsics a:nd management 

moan^ is taken for inixii\ii- ihoni with tho !<oil tlu\Y lUwuiposo 
almi>!?t eiitin^lv, loaviuir littlo luvuv than tho ash of the plant to mix 
with the s<.>il. Even if this mixing weiv not neivssavY the veiivhible 
material wonUl interfere with enltivation if left on tlie siirfa^w 
The plow is tlie best implement for eovejing all org?inie material, 
sueh as t rop rosiduos. weeds, and farmyard maiiniv. 

3. Killing Weeds. — A most important objeot of tillage is kill- 
ing weeds. We set^ demonstrations evervwhere of the faet that ordi- 
naxv en^ps amount to verv little when in i\mipetition with wee<ls. 
A weed is a Ivtter forager than a eultivated plant, and hetnv will 
deprive it of Kuh moistuiv and food, and it is neeessarv for sne- 
cessful erop produetion that the wtvds be destroyed. Tillagv is the 
best means so far devised for aeoomplishing this purpose. li\ some 
eases, however, sprays have been used sneeessfuUy. and if sprays 
innild be found whieh would not injure the erop. but would kill the 
wtvds. there is no question but that mueh of our tillage eould l>e 
disjionsed with. 

4. Storing and Conserving Moisture. — ^Plants require an 
abundant supply of moisturo for il\oiv gonnmation and growth. In 
nearly all elimates thrvnigh uneven distribution of rainfall the neees- 
sitv exists for storing moisture in the soil when it can be obtained 
and for conserving this for the use of the crop later. The early 
preparation of the soil by loosening and tHUupaeting slightly is the 
best means for storing the supply of this for futuiv use. Ltx>sening 
the soil allows rapid al>sorption with little run-otf. while stirring 
the surface soil later prevents any excessive loss through evapora- 
tion. Of these two under ordinary humid ixuulitions, the prepara- 
tion of The soil for storing the moisture is of much more iniporta*iee 
than subsequent tilla^ for retaining it when a erop is growing. 
Previous to t]\o planting of the en^p the soil shotild lx» kept stirred. 

5. Compacting the Soil. — It freipiently Ixwuues nci'ossjiry 
after a soil has l>een plowed to compact it in order to close any 
large air spaces that may exist in the plowed soil and also bring the 
furrow-slii\e in close cvuitaet with the soil beneath it so that capillary 
action may not W cut otf. At the same time that the i\unpaeting 
is done the soil should Iv pulverized, thus making a better svvd bed 
for the crop. 

tn Planting the Seed. — ^While theiv is not nmoli of what we 
usually oall ullage in the ordinary stH\lii\g of crops, yet all seeding 
is accompanied by more or less working of the soil. 



TI I.LAC H'] 327 

IiMIM.KMION'l\S 01'' TIM.ACJIO 

'^rillu^n; iiTi|)l(!rn(!iil,H ar(j (JividcMJ iiiio (Ivc (;I}ikh(!,s — [)1()wh, liiir- 
rowH, (;()iii|):i(;L(;i'H, scu'dcrs, find ciiltivJiioi'H. 

I. Plows." '\'\\(' iiKild Ituiird |)li)vv is Olid of IIk; inosl, (•oiiiinon 
iis W(;ll as Olio of llic licsl, iiiinlcinciils fur loosnniii'r ilic; soil iuid 



A I', <: 

Fia. I.'i7. — liiiiKriiiri HlinwiriK ^^\(^. i\\(:(ir(;i]r.!i,\ tict.'uin of l.hc plow. 'I'lii; Hlidi/iK or HlKiarin^ is 
acco/npuriiod by iriorc or I^hh of a rolling uclioii, all of wliicJi pulvorizoH the Hoil. (KiriK.) 

turning ujidor vegeiabJe material. It briM^s about almost a com- 
plete inversion of the furrow-sliec!, and in doing tliis pulverizes the 
soil. 'J'he mold-board is of such a curvature that when the soil 
passes over it, it produces a sliearing force in the soil as if made up 
of different layers somewhat similar to the effect of hending several 
leaves of a hook and lirings ahout pulverizaiion (Fig. 137) if the 




A n c 

Fio. 138. — SliowinK th(; Uiroo types of mold-hoanlH. A-Hod. li-Gonoral pur|)OH(;. 

C-Stubhlo. 

soil is in good condition for plowing. If too dry so that the soil 
is cloddy little pulverization is accomplished. If the soil is too wet 
for plowing this shearing hreaks down the granules, producing par- 
tial puddling, very injurious to the soil. The plow should be set 
so that the furrow-slice will he cut free from the soil heneath and 
practically all inverted. Mold-hoard plows are divided into stuhhle, 
general purpose, and sod plows. 



328 



SOIL PHYSICS AND MANAGEMENT 



The stubble plow (Fig. 138C) has a short, strongly curved 
mold-board and is probably the best form to use in old land. In 
general the more curvature or twist there is to the mold-board the 
greater the pulverization, the better is the condition of the soil after 
plowing, provided it has the proper moisture content. This plow 
is not desirable to use in breaking sod, because of the rough con- 
dition in which it leaves the surface. The jointer is sometimes used 




Fig. 139. 



-Plow with separate jointer and rolling coulter attached ready for use. 
Plow Company.) 



(Molina 



in the plowing of light sods, as it materially aids in turning under 
and preventing the further growth of grass (Figs. 139 and 1-iO). 

The general purpose plow (Fig. 138B) is a form intermediate 
between the stubble and sod plows in length and curvature of mold- 
board. It may be used for either stubble or sod. It does not pul- 
verize the soil so thoroughly as the stubble mold-board, and as a con- 
sequence it leaves sod in much better condition for working into 
a good seed bed. For all uses it is probably the best. 



TILLAGE 



329 



Sod plows (Fig. 138A) have long, slightly curving mold-boards 
that do the minimum amount of pulverization in turning the fur- 
row-slice. They are used principally in 
the plowing of tough grass sods, since 
they turn the furrow-slice without 
breaking it very much, thus leaving a 
comparatively smooth plowed surface. 
This has some advantages in the pro- 
duction of a seed bed, 

A form of the mold-board plow 
known as the hillside or sivivel plow 
may be reversed so that the soil may 
all be thrown in one direction. 

The disk plow (Fig. 141) may be 
used under some conditions to good 

advantage. If the soil is quite com- Fig. 140.— The combined jointer 
„i„in-j 1 Ti •! and rolling coulter is a good attach- 

pact and dry it may be used where it ^ent for aii plows. (MoUne Plow 
would not be possible for the mold- Company.) 
board to do any work at all. It has this other advantage, that it 
does not tend to produce a plowpan, because the furrow-slice is 





Fig. 141. — Disk plow. (Moline Plow Company.) 

broken off rather than cut off. Under some conditions it turns 
rubbish under better. Disk plows are extensively used in arid and 
semi-arid regions, but may be used successfully on almost any soil. 



330 



SOIL PHYSICS AND MAXAGE:iIE^■T 




Fig. 142. — Lister for preparing the ground and planting corn. Used chiefly in the semi- 
arid regions. (Moline Plow Company.) 

A reversible disl- for hillside plowiug has some advantages over the 
ordiuary reversible mold-board plow. 

A deep tilling, double disk plow for stirring the ground to a 
depth of 16 to 18 ineiies is used in some sections. This does not, 
however, bury the surface soil to so great a depth as would be indi- 
cated, hut mixes this deeper soil with the surface to a greater or less 
extent. The disk plow cannot be used in stony land successfully, 
particularly where the stones are firmly set in the soil. 

The lister (Fig. 1^2) is a plow used particularly in semi-arid 
regions for the preparation of the ground for corn planting, and 
even for other crops. It is a double mold-hoard plow, and when 
used opens a furrow in which the corn is planted. It ridges the 
land and gives the soil an excellent chance to weather (Fig. 1-43). 

The subsoil plow (Fig. Ill:) is used to loosen the soil in the 
bottom of a furrow made by the ordinary plow. It consists of a 
shoe which merelv raises the soil, but does not throw it o\it. 



TILLAGE 



331 



^./ji 




Fig. 144. — Subsoil plow. 

2. Harrows. — The spike-tooth harrow is the form commonly 
•used and is very effective in pulverizing and slightly compacting 
freshly plowed land. In some places the " A " harrow, with square 
teeth, is still extensively used, and is especially desirable in stumpy 
land. The lever harrow (Fig. 145) of two to four sections is very 
commonly used, sometimes with a riding attachment. The levers 
permit the slanting of the teeth so that any rubbish will easily pass 
out of the harrow. 



332 



SOIL rUYSlCS AND MANAGEMENT 




Fig. 145.— Spike-tooih harrow 




Fia. l-lt". — Spnng-tootii harrow. 

The spring-tooth harrow (Fig. 146) is used quite exteusivelv 
in r;.uJ-I°re the soU is in iatl«v poor pliys.cal oomht.ou a^d 
"here it is neoessarv to cultivate as ^ell as harrow. After a ram 



TILLAGE 



333 



this harrow will do more ciVutmit work in loosening the soil than 
the ordinary spike-tooth harrow, and for that reason is a«ed mostly 







iuj. H7 — AciKft blade harrow. 




Fig. 14S. — The isolid dwk. 



on soils that are deficient in organic matter. It is a ver}' good imple- 
ment to u.-e in the cultivation of alfalfa. 

The Acme or blade harrow ( Fig. 147 ) is used to some extent, 
and is an excellent implement to pulverize and compact the soil. 



534 



SOIL PHYSICS AND MANAGEMENT. 



The bar in front, if properly adjusted, crnslies clods," while the 
twisted blades stir the soil and destroy any weeds that may haye 
started. For this purpose it is better than the spike-tooth harrow. 




Fig. 149. — The-cut away disk. 



00^ 




Fig. 150. — The spading disk harrow. 

The disk harrow (Figs. 148, 149 and 150) is made in three 
forms — the solid disk, the cut-away, and the spading disk. The first 
two act somewhat the same as the disk plow, but do not turn the 
dirt so thoroughly, yet are very effectiye in stirring the soil. The. 



TILLAGE 



335 



degree of effectiveness, however, may be increased or diminished by 
adjusting the angle of the disk with the direction of movement. 
Next to the jjIow the disk is one of the most important and useful 
implements. It may be used very effectively before the plowing is 
done, and is one of the best tools for the preparation of a seed bed. 
Either the solid disk or the cut-away may be used to excellent 
advantage in cutting up corn-stalks and other vegetable material 
and mixing them with the soil before plowing. This insures the 
close contact of the furrow-slice with the soil beneath. A small 
rotary spading harrow is sometimes attached to the plow. 




1 iG. 151. — Smooth or drum roller. 

3. Compacters. — Compacting is necessary because most of our 
crops require a firm but mellow seed bed. In many cases in our 
heavier soils clods are formed which require the use of the roller 
to crush, while in the case of sands, sandy loams, and many silt 
loams the soils are so loose that root development and moisture 
retention are interfered with. In arid and semi-arid regions the 
subsurface compacter is used to prevent the excessive loss of moist- 
ure through any large air spaces that may exist in the soil. The 
packing also increases upward capillary movement of soil moisture, 
and consequently less water is lost by the downward movement. 

The smooth or drum roller (Fig. 151) is used quite exten- 



336 



SOIL PHYSICS AND MANAGEMENT 



sively, but is not as effective as some other forms and is gradually 
being replaced. When used for crushing clods these are frequently 
pressed into the soil without being affected to -any extent, and a 
subsequent harrowing before a rain usually brings them to the sur- 
face again. Its use greatly increases evaporation of moisture. 




' U^^^'^A 



r*^^ ^ "' 

r ^^s. 



,-*5, 






^Um 







FlG. l.j:J. — Di,-,k drill aud its work. 



Corrugated Roller. — The smooth form of roller is gradually 
being displaced in the corn belt by the culti-packer or corrugated 
roller (Fig. 152), which consists of a series of wheels with a sharp 
ridge about two to two and one-half inches in height. This imple- 
ment is much more effective in crushing clods and leaves the ground 
covered with a thin mulch. 



TILLAGE 



337 



The bar roller is another form, made up of a series of bars 
running lengthwise of the roller. This implement is better than 
the ordinary drum roller, but is not as effective as the corrugated 
roller or culti-packer. 

Flankers made by bolting together two or three two-inch 
boards so that they lap about half may be used to good advantage 
for crushing clods and levelling without compacting to any extent. 

The Campbell subsurface packer (Fig. 107, page 2i7) is 
used in arid and semi-arid regions. Its special advantage is that 
it compacts deep, freshly plowed soil, leaving a- mulch on the, sur- 
face. It consists of a number of wheels with a wedge-shaped edge. 
These are about five inches apart and revolve independently of each 
other. As this wheel presses in, the soil is pushed to both sides, 




Fig. 154. — Press drill 

thus closing the air spaces, leaving a loose mulch on the surface. 
This may be used in sandy soils in humid regions to very good 
advantage. 

4. Seeders (Figs. 153, 154, 155). — The tillage done by seeders 
is purely incidental, yet in many cases very essential. Drills almost 
invariably till the soil to a considerable extent in opening a furrow 
every six to eight inches in which to deposit the seed. Where press 
drills are used the soil is compacted upon the seed. In the planting 
of corn with the ordinary planter the tillage is similar to that of the 
press drill, but not so extensive. Many broadcast seeders, how- 
ever, accomplish no cultivation. 

5. Cultivators. — Cultivators are for use in intertilled crops. 
Some stir the soil to a depth of one inch or less, while others work 

22 



338 



SOIL PHYSICS AND MANAGEMENT 



to a depth of four inches or more. They ma}- be divided into shovel, 
disk, blade cultivators, and weeders. 




FiQ. 155. — Ordinary corn planter with attachment for planting cowpeas in hill or row with 

corn. 



*~- "»,~\ 




Fig. 156. — Three-shovel cultivator. 



The shovel cultivators (Fig. 156) vary in the number and size 
of the shovels used. There may be two large shovels on each gang, 
three medium, or four small ones. The depth to which they go 
varies directly with the size of the shovels. It is not unusual to 



ULLAGE 



339 



see cultivaiion done over lour indies (l('('|) willi the ]ar<(o or rn(;(liiim 
sliovcl. There are two types ol' cultivators with four or five small 
shovels iji each gang — the eagle claw and the spring-tooth. 'IMicse 
])en(!trate the soil to a depth slightly more than two inches. A form 
of the shovel plow is made hy replacing the inside; shovel with a 
little diamond or har share plow hy which the soil is thrown up 
into a high ridge along tlie corn row. 

The disk cultivators (Fig. 157) consist of three disks on each 
side and may he used to good advantage where the hind weed or 
wild morning glory ahounds. As these cultivators are commonly 
used the disks are set to run deep and corn-row ridges result. They 




Fig. 1.57. — Disk cultivator. 



Fig. 1.58. — Surface or blade cultivator 
with leveler. 



may, however, be adjusted to Tun shallow and leave the soil com- 
paratively level. 

Blade cultivators (Fig. 158) consist of four blades, two to 
each gang, from 1;^ to 18 inches long and two to three inches wide. 
These are placed at an angle such that there is a slight tendency 
to move some soil toward tlie row, but most of it falls over the blade, 
leaving a loose mulch. This implement is very satisfactory for 
shallow cultivation, and may be so adjusted as to stir the soil to a 
dejjth of three inches or more. Cultivation to this depth, however, 
is seldom advisable because of the injury to the roots. The blades 
cover the entire space between the rows, so there is very little chance 
for weeds to escape. " A '^-shaped blades are being used to some 
extent. The sweep is a modification of the blade cultivator. Each of 
the above is made in Ixjth one- and t\vo-row forms. Various imple- 
ments for use with one horse are found, such as the double-shovel, 
the five-shovel, and fourteen-tooth cultivators. 



340 



SOIL PHYSICS AND MANAGEMENT ' 



The weeder (Fig. 159) consists of a large number of narrow 
spring teeth well adapted for shallow cultivation of such crops as 
corn, cowpeas and beans in humid sections and for most of the 
crops in semi-arid regions. For this implement to do its best work 




Fia. 150. — Wccdcr. 

tlic soil should be mellow and in good tilth and the weeds small, 
but if the soil is compact or the weeds quite large it is of little value. 

PLOW^ING 

Plowing is an art. It is one of the most important as well as 
the most common motliods of preparing the soil for the crop. From 







Fig. 100. — An early form of plow. 

the beginning of agriculture some form of plow has been in use. 
Even at the present time in some countries the plow is a very primi- 
tive implement, as shown in Fig. 160, and does very inefficient work. 
In North America we find the two extremes. In parts of Mexico 
the people are still using the most primitive form of plows. In the 



TILLAGE 



341 



wheat region of the northwest the powerful trnetor, with its six to 
ten plows and accompanying dislvs and harrows, may he seen jn'e- 
paring the soil for the crop. These improvements have materially 
reduced the cost of raising a hnsliel of wheat. In the southern jiart 
of the United States many one-horse plows are used. Plowing, 
when w^ell done, accomplishes moi'(^ ol' tlu> ohjects desiivd in tillage 
than any other operation. The plowing done hy the crude imple- 
ments of })rimitive peoples falls far short of good results. It enahles 
them, however, to put their soil in somewhat hetter condition, and 
without douht they grow larger crops than without even this simple 
operation. 




Fi(3. IGl. — Tlic sod is well (unicd nnd n-prosnnts Rood work. 

Cood ])lowing sa\es lahoi' in the prcpai'at ion of a s(H'd hed. it 
gives all ])lants ol' the crop an equal chance and all a much greater 
advantage than on poor plowing. For good plowing the following 
things are essential : 

1. The entire furrow-slice should he cut loose from the soil 
heneath and all turned. In other words, "cutting and covering" 
is not good plowing. 

2. The plowing should he done to a certain depth to produce 
pulverization. In most cases the soil is not pulverized to any extent 
when the furrow-slice is oidy three or four inches thick. For hest 
pulverization plowing should he done five to seven inches deep. 



342 



SOIL niYSlCS AM> MAXAGEMENT 



0. The turning under ot' rubbish is essential to good plowing. 
To do this properly the furrow-diee must be five or six inehes thiek, 
and in some eases ehains or \vt.H>d hooks are necessary. 

4. The furrow should be kept straight or at least parallel with 
the middle ridge, as a crooked furrow almost always indicates 
'' cutting and covering " at some points. 

1. Time of Plowing. — The time when plowing sliould be done 
varies with climatic, crop, and soil conditions. In scini-;irid regions 




Fi.-,. u;-\ 



M. -hino Ct^mi^rtnv.'V 



W" 




Fl«. loo, — .\ orooktxl furrow diH^s uoi look well, even if ihe plowins is s>^«.Hi. 



TILLAGE 343 

plowing should follow the preceding crop as soon as possible. The 
primary object to be accomplished is conservation of moisture. In 
humid regions the time of plowing depends upon the crop to some 
extent. The plowing for wheat and rye must be done in summer, 
while for corn, cotton, oats, barley, cowpeas, and soybeans it may 
be done either in fall or spring. 

(a) Fall Plowing. — If the plowing is done in the fall the 
ground should be plowed as late as possible unless a catch crop is 
planted to conserve the available nitrates. When the ground is 
stirred by the plow it produces conditions very favorable for nitrifi- 
cation, which takes i^lace at the expense of the organic matter in the 
soil, resulting in the production of soluble plant food that may be 
leached out of the soil during the vianter and spring. If a catch 
crop is grown the plants take up the soluble plant food and preserve 
it. In the case of very late fall plowing the conditions are usually 
not favorable for any large amount of nitrification, and the result is 
that little soluble plant food will be formed before winter. 

The soil never becomes too dry to be plowed in the fall when 
looked at from the standpoint of benefit to the soil. It may become 
so dry, however, that it will be impossible from a power standpoint 
to do the work with horses. The tractor may be used to good advan- 
tage under these conditions. 

There are several important advantages in fall plowing : first, the 
work may be done at the time of the year when other work is less 
pressing; second, the organic matter turned under during the fall 
has sufficient time to partly decay before the crop is put in, thus 
liberating the plant food and giving the soil time to settle and re- 
establish capillary connection; third, many insects and their eggs 
are destroyed by disturbing them late in the fall, which is especially 
true of the ant hills containing the eggs of the corn root aphis; 
fourth, the improvement of the tilth of the soil by exposing it to 
freezing and thawing and wetting and drying during winter and 
spring, producing a granular condition that is very desirable. This 
is especially true of heavy soils containing a fair supply of organic 
matter. 

As a general rule, soils deficient in organic matter do not re- 
ceive as much benefit from fall plowing as soils well supplied with 
this constituent. If deficient in organic matter, freezing and thaw- 
ing cause the soil to run together instead of producing granula- 
tion. Timber soils generally are not as well adapted to fall plow- 



344 SOIL PHYSICS AND MANAGEMENT 

ing as prairie soils because of the lack of organic matter. Even 
the lighter colored phase of brown silt loam packs badly during 
winter. If fall plowed, sandy loams are liable to be damaged bV 
blowing. Heavy soils are especially benefited by fall plowing. 

(b) Spring Plowing. — A very large amount of plowing must 
necessarily be done in the spring because the crop of the preceding 
year was not taken off in time for fall plowing. It is very essential 
that some preparatory work be done previous to the plowing. This 
should usually consist of thoroughly disking (Fig. 16-i) the ground 
to cut up the vegetable material and mix it with the soil so that, 
when the furrow-slice is turned and compacted slightly, close capil- 
lary connection may be established at once. Where corn-stalks are 
to be turned under, as is frequently done in the corn belt, the cutting 




Fig. 164. — Previous to plowing, disking should be done to cut up the corn-stalks or other 
vegetable matter and produce a deep mulch. 

up of the' stalks by the disk is a very important process, since when 
plowed the fine soil filters in around the stalks and does not permit 
the formation of large air spaces that aid in drying the soil. This 
disking will also prevent evaporation, so that if plowed later it will 
be comparatively free from clods. 

2. Depth of Plowing. — Poor and badly-worn soils should be 
plowed deeper than rich, productive ones. Our cereals and grasses 
are shallow rooting plants, the major part of the roots developing 
in the plowed soil. This forms their natural and most accessible 
feeding area. Within certain limits the deeper the plowing the 
better the chance of the crop for getting an abundance of food. 
If the plowing is done too deep the surface soil Avith its swarms 
of bacteria will he buried below the zone of most favorable action 
and a smaller amount of available food will be developed for the 



TILLAGE 345 

crop. Experience indicates that eight or nine inches is about 
the limit. For rich, deep soils six to seven inches is sufficient. This 
gives a deep reservoir for water storage and an abundance of soil 
for root development. 

Deep Tilling. — Deep tilling plows have been put on the market, 
by which plowing may be done to a depth of twelve to eighteen 
inches. As a result of nine tests for corn, the yield was 2.7 bushels 
higher for ordinary plowing than where plowed twelve to fourteen 
inches deep. This may have some advantages for alfalfa and other 
deep-rooting crops. The Kentucky Station found an increase of 
416 pounds of alfalfa hay in two cuttings in favor of deep tilling. 

Subsoiling.— Subsoil plows have been used for loosening the 
soil to a greater depth than is possible with the ordinary plow. This 
practice was more common a few years ago than at present. The 
results do not indicate that the operation in humid soils is of very 
much value. As a result of 40 tests in southern Illinois the sub- 
soiled land gave an average of 2.7 bushels less than the land not sub- 
soiled.^ This practice may have some value in semi-arid regions and 
for certain crops, but it is certain that it has very little value for 
the principal cereal crops in humid regions. 

Dynamiting. — The use of dynamite for breaking up the im- 
pervious or hardpan subsoils has been resorted to in some cases. 
This is a good practice where trees are to be planted. A charge of 
dynamite is exploded and the tree is planted in the loose soil thus 
produced. The expense involved in breaking up the subsoil in this 
way makes the practice almost prohibitive for ordinary crops, unless 
the increase in yield is much greater than the experiments up to 
the present would indicate. 

Effect of Deep-Rooting Crops. — Without much doubt nature 
has provided the best method of deep tillage. This is by means of 
deep-rooting plants, and more especially legumes. A crop of red, 
mammoth, sweet clover or alfalfa fills the soil with roots and leaves 
it open and readily permeable to water and air. These roots extend 
to a depth of several feet and render heavy clays pervious, bring 
plant food from the subsoil to the surface, and benefit such soils in 
various other ways. The crop should be seeded much thicker than is 
done ordinarily. There should be from six to twelve or more plants 
to the square foot, as one plant to the square foot is of comparatively 
little benefit. 

Preparation of the Seed Bed.— The ordinary farm crops re- 
quire better conditions for their growth than the wild plants with 



346 



SOIL PHYSICS AND MANAGEMENT 



which we are familiar. The soil in which they grow must be suf- 
ficiently loose so the roots have little ditiiculty in penetrating it. 
The gro'W'th they make depends to a large extent on the area over 
which the roots spread. Hence the necessity of producing a deep, 
mellow seed bed that will allow free root development. 

Clods are of no value in a field, but are always a source of annoy- 
ance. They are generally the jDroducts of shiftless and unscientific 
methods of farming rather than of some inherent fault or bad 
quality of the soil. Soils if worked at the proper time and after 
proper preparation respond to good tillage. The disk is one of the 
best implements for preventing the formation of clods and, to- 
gether with the culti-packer, for destroying them if they once form. 

0^. 




Fig. 165. — Grain produced from five tenth-acre plots prepared in different ways for winter 
wheat. (L. E. Call.) Kansas Station. 

Clods are of no use to a growing crop,- but on the contrary lock 
up large quantities of food and become prisons for millions of bac- 
teria that would otherwise be working for the farmer. Fields are 
sometimes seen in which at least one-third of the plant food of the 
plowed soil is locked up in clods. Even if the clods are turned 
under and covered by mellow, moist soil, weeks are required before 
they become thoroughly moistened unless rain falls. 

1. Wheat. — Plowing for wheat should be done as soon as pos- 
sible after the removal of the preceding crop and from five to seven 



TILLAGE 



347 



inches deep. If the ground is dry or liable to become dry before 
plowing can be done clods may be prevented from forming by 
thorough disking. This kills weeds and produces a mulch which 
conserves moisture and later jDlowing may be done very satisfactorily 
without any great amount of clods. The impression prevails that 
since wheat is a very shallow rooting plant the plowing should be 
done somewhat shallow, but experiments show that a depth of seven 
inches is not too deej) (Fig. 165). Immediately after the plowing 
is done it is necessary to work the soil by means of a disk and harrow 

Methods of Preparing Land for Wheat ^ {Continuous Wheat) 



Alethod of preparation 



Average of 3 years, 1911-1913 



Yield per 
acre, bushels 



Disked, not plowed 

Plowed, Sept. 15, 3 inches deep 

Plowed, Sept. 15, 7 inches deep 

Plowed, Aug. 15, 7 inches deep 

(worked) 

Plowed, Aug. 15; 7 inches deep, not 

worked till Sept. 15 

Plowed, July 15, 3 inches deep 

(worked) 

Plowed, July 15, 7 inches deep 

(worked) 

Double disked July 15, plowed 

Sept. 15 

Double disked July 1 5, plowed Aug. 15 

7 inches deep 

Listed July 15, 5 inches deep, ridges 

split Aug. 15 . 

Listed July 15, 5 inches deep ; worked 

down 



6.63 
13.24 
14.15 

22.19 

I 20.48 

20.77 

27.11 

19.71 

23.40 

22.90 

22.77 



Cost per acre 
for preparation 



$2.07 
2.83 
3.33 

4.00 

3.33 

4.85 

5.35 

3.93 

4.93 

3.92 

4.05 



Value of crop 
less cost of 
preparation* 

•$3.64 
8.35 
8.60 

16.34 

13.65 

12.25 

16.87 

12.37 

14.30 

14.73 

14.53 



* Wheat market value when threshed. 

to conserve moisture, develop plant food, and, most important of 
all, prevent the growth of weeds. The seed bed for wheat must be 
firm. If the soil is very open at seeding time the freezing in winter 
will have a greater tendency to heave the soil and kill the wheat, 
especially if the land is not well drained. The roller or culti- 
packer can be used to excellent advantage in the preparation of the 
seed bed for this crop. 

In seeding wheat in corn ground after the corn has been taken 
off the field for the silo, or placed in the shock, a sufficiently good 
seed bed may be produced with the disk. The settling of the soil 



348 SOIL PHYSICS AND MANAGEMENT 

during the summer will make it sufficiently compact and a thin 
stratum of two to four inches in depth mellowed somewhat by the 
disk will provide an excellent seed bed. Wheat is sometimes seeded 
in the standing corn and in such case no preparation is necessary. 
The crop is handicapped, however, because the corn has left the 
soil in poor condition in regard to moisture and plant food. 

The preceding table shows that deep, early plowing with working 
till seeding time has given the greatest profit. 

The soil for wheat should be well drained. This is very essential, 
especially in temperate regions where freezing and thawing occur. 
The great objection to growing wheat formerly was the winter killing 
caused by a poorly drained seed bed. 

2. Corn. — The plowing for corn may be done either in fall or 
spring and the production of the seed bed is somewhat different in 




Fig. 166. — ^A good seed bed on stalk ground. 

the two cases. With fall plowing the ground should be disked or 
worked in some way as early as possible in the spring to a depth of. 
three to five inches. This conserves moisture, raises the temperature 
of the soil and destroys any weeds that may have started. This 
disking should be continued at intervals of ten days or two weeks 
until the time for planting. The object is to destroy as many 
weeds as possible before the crop is planted, as cultivation for this 
purpose is much more effective at this time. The disking should 
be done deep to thoroughly aerate the soil and encourage the develop- 
ment of plant food. Corn on fall-plowed land is said by some 
farmers to " fire " easily. This " firing " may be due to two causes : 
first, to lack of moisture, and, second, to lack of available nitrates. 
Fall plowing, unless the soil is in good tilth, tends to dry out early 



TILLAGE 349 

and rapidly. The rains have compacted it, the ground is bare, and 
with the strong winds of March and April there is nothing to prevent 
rapid loss of water. Deep, early disking in the preparation of the 
seed bed will conserve moisture and in this way tend to eliminate 
this danger from " firing." Thorough and deep disking also en- 
c( urages the formation of large quantities of available nitrates. In 
the case of shallow and insufficient disking the fall-plowed land is 
left compact and somewhat cloddy, with conditions for nitrification 
and conservation of moisture very unfavorable. Such preparation 
has a tendency to encourage " firing.^' 

The preparation of the seed bed from spring-plowed land does 
not require so much working during the average season as for fall- 
plowed land. The ground should be thoroughly worked with disk 
or harrow immediately after plowing. A rotary harrow attached 
to the plow does good work. This working should be continued at 
intervals the same as for fall plowing. When ready to plant, the 
harrow may be sufficient to put the soil in fine condition (Fig. 166). 
All weeds should be killed. If very few rains occur in the spring 
after plowing is done it may be necessary to use the roller, since 
corn, like wheat, requires a firm seed bed with a mellow surface. 
Too much work can never be done in the preparation of the seed 
bed. The best time to destroy weeds in corn is before the crop is 
planted. The cultivation at that time is much more efficient than 
at any time thereafter. 

3. Oat?. — The almost universal practice in the corn belt is to 
sow oats where corn grew the preceding year. It was an early 
practice in some regions to sow the oats in February or March 
without preparing any seed bed whatever. Sometimes fairly sat- 
isfactory results were obtained. But as the physical condition of 
the soil became poorer th'e necessity for a better seed bed for the 
oat crop has become more imperative. A very good way for pre- 
paring the ground for oats is to plow it in the fall and then disk 
thoroughly in the spring. In the corn belt, however, the apparent 
necessity for pasturing the corn-stalks does not favor this prac- 
tice. Oats do not require a deep seed bed, but it' should be well 
prepared. The common practice in the corn belt is to disk the 
ground from one to three times and give it a final harrowing. 
The oats may be seeded at any time, either before the first disking or 
between the two diskings. Even in the best of soils one disking is 
not sufficient, although this is not an uncommon practice. The 
stalks to a certain extent prevent the full efficiency of the disk and in 



350 SOIL PHYSICS AND MANAGEMENT 

many cases a considerable portion of the oats are not covered, being 
in some cases by actual count one-eighth of the amount seeded. 

Plowing the ground before seeding aids in jDroducing an ex- 
cellent seed bed; however, it will be too loose unless thoroughly 
firmed. The harrow and compacter should be used, and if the 
soil is well supplied with organic matter so it will not bake it 
should be rolled after the seeding is done. The«disk drill has some 
advantage over the broadcast seeder for seeding oats, and the fact 
that it covers practically all the seed is a decided advantage. Only 
about two-thirds as much seed will be required as when seeded 
broadcast. 

Cultivation. — Object. — The objects to be accomplished in the 
cultivation of a crop are : first, and primarily, the killing of 
weeds; second, the conservation of moisture; and, third, aeration. 
While the conservation of moisture has usually been placed first, 
recent experiments show that cultivation for the killing of weeds in 
humid regions is of vastly more importance to the crop than for 
the conservation of moisture. It is a question whether this may 
not be true in semi-arid regions as well. Weeds require both 
moisture and plant food for their growth and are much better for- 
agers than the cultivated crop. At the Illinois Station (table, page 
352), as a result of nine years' investigation, corn with weeds de- 
stroyed by a hoe without producing a mulch gave a yield of 48.9 
bushels per acre for a nine-year average, while for the same time 
corn in which weeds were allowed to grow produced 7.5 bushels per 
acre, or 41.-i bushels in favor of preventing the growth of weeds 
(Figs. 167, 168, 169). In order to determine whether it was the 
lack of the plant food or the moisture that caused the greater loss, 
part of each plot in v/hich the weeds were allowed to grow was sup- 
plied with all the moisture the crop and weeds needed, and as a five- 
year average the yield was increased 2.5 bushels over the plots where 
no water Avas applied. This shows rather conclusively that the 
greatest loss was caused by depriving the corn of food. 

Value of the Mulch. — In this same experiment the plots men- 
tioned above in which the weeds were kept down with a hoe with- 
out producing a mulch gave a yield of 48'.9 bushels, while the corre- 
sponding plots which were cultivated gave a yield of 43.3 bushels, or 
5.6 bushels were lost due to damage by cultivation. Moisture de- 
terminations in each of these three plots were made and it was 
found that the amount of moisture in the uncultivated plot actually 
exceeded that of the cultivated by 0.3 per cent for an eight-year 



TILLAGE 




Fig. 167. — Nine-year average yield 43.3 bushels per acrp. 




Fig. 169. — Nine-year average j-ield 7.4 bushels per acre. 



352 



SOIL PHYSICS AND MANAGEMENT 



average. It is without doubt true tliat if the ground is plowed to a 
depth of six or seven inches, and a good seed bed produced, there 
is very little necessity for cultivation of corn on silt loams and 
sandy loams to conserve moisture. It will be seen from the following- 
table that during the dry yearg of 1911, 1913, and 1914 the yield of 
corn on the uncultivated plots was 5 to 10 bushels more than on 
the corresponding cultivated ones. The mulch should have had its 
greatest effect during these seasons if it was of much use in con- 
serving moisture for the crop. 

Results of Cultivation of Com ^ — Each is an Average of Two Plots (Bushels 

Per Acre) 



Treatment 


1906 


1907 


1908 


1909 


1910 


1911 


1912 


1913 


1914 


1915 


9-year 
average 


Average* 
per cent 
of No. 5 


1. Not plowed nor cul- 

tivated, weeds 
kept down by 
scraping with hoe 

2. Plowed, seed bed 

prepared, no cul- 
tivation, weeds 
kept down by 
scraping with hoe 

3. Plowed, seed bed 

prepared, weeds 
allowed to grow 

4. Plowed, seed bed 

prepared, weeds 
allowed to grow. 




38.3 

44.0 
0.0 


25.0 

33.0 
16.0 


28.6 

50.7 
10.2 


33.1 

40.5 
.4 


25.5 

39.8 
.9 

2.6 
34.5 

55.0 
77.3 


46.1 

75.5 
7.9 

11.5 
65.2 

61.2 
q3 


16.5 

34.0 
10.4 

12.3 
21.9 

41.2 
50 6 


38.5 

50.0 
12.3 

20.4 
40.5 

56.2 
.56.1 


64.9 

72.9 
8.6 

5.9 

76.0 

70,4 

72.0 


35.2 

48.9 
7.4 

10.5t 
43.4t 

50.21: 
74.9s 


81.3 

112.9 
17.1 

22.8 


5. Plowed, seed bed 

prepared, culti- 
vated 3 times 

6. Plowed, seed bed 

prepared, culti- 
vated 3 times, 
irrigated 

7. Plowed, seed bed 

prepared, culti- 
vated 3 times, 
irrigated, fertil- 


44.7 
46.2 

69.7 


49.6 
49. S 

102.2 


25.0 

28.2 


31.4 
40.0 


45.7 
50.3 

78.3 


100.0 
115.5 

158.4 















* Based on all comparable yields, 
t Five-year average, 
i Ten-year average. 
s Eight-year average. 

The cultivation was done so as to produce a mulch from 21/0 to 
31/4 inches in depth. (See Figs. 170 and 171.) During the years 
mentioned the mulch was so dry and loose that the roots of the 
corn did not penetrate it, so that if it had any value at all it was in 
conserving moisture. The corn roots generally develop most abun- 
dantly in the plowed soil. By cultivating three inches deep the crop 
was enabled to use only one-half of the plowed soil, and there was 
no doubt that the stirred soil was worth more to the crop for the 



TILLAGE 



353 



plant. food it contained than for the moisture it conserved. The 
experiment was conducted on the brown silt loam, the common 
corn-belt soil of Illinois. The same experiment was tried on 
the gray silt loam on tight clay with somewhat similar results, as 
shown in this table : 

Resiilts of Cultivaiion of Corn on Gray Silt Loam on Tight Clay at Fairfield, 
Wayne County,* Illinois {Yields in Bushels Per Acre) 



Treatment 


1908 


1911 


1912 


1913 


1914 


3-year 
average 


5-year 
average 


Average 
percent 
of No. 4* 


1. Not plowed, not culti- 


















vated, weeds kept down 


















by scraping with hoe 


4.0 


3.2 


22.8 


0.0 





10.0 


6.0 


31.4 


2. Plowed, seed bed pre- 


















lared, weeds kept down 


















by scraping with hoe 


16.7 


22.1 


55.6 


0.0 





31.5 


18.9 


98:9 


3. Plowed, seed bed pre- 


















pared, weeds allowed 


















to grow 


8.1 


8.7 


14.6 


0.0 





10.5 


6.3 


33.0 


4. Plowed, seed bed pre- 


















pared, cultivated 3 


















times 


23.8 


24.0 


45.8 


2.1 





31.2 


19.1 


100.0 


5. Plowed, seed bed pre- 


















pared, cultivated 3 


















times, manure, rock 


















phosphate, limestone 


41.5 


32.6 


62.1 


14.6 





45.4 


30.2 


158.1 



* Computed from 5-year average. 

The Department of Agriculture ° reports a number of experi- 
ments somewhat similar to this, and the average yield of corn on 
the uncultivated plots was 52.6 bushels, while that of the cultivated 
was 52.5 bushels per acre. These were conducted on various kinds 
of soils in 28 different states. The necessit}'' for cultivation is 
greater on heavy soils than on light ones. This is shown by the 
fact that uncultivated sandy loams and silt loams produced 105.7 
per cent and 102.4 per cent of the cultivated, while the clay loams 
and clays produced, respectively, 94.5 per cent and 92.6 per cent 
as much as the cultivated. When the crop becomes large enough to 
partly shade the soil, and the roots become thoroughly distributed 
through the soil, there is very little necessity for cultivating to 
conserve moisture. The water that moves upward is captured by 
the roots before it reaches the surface and evaporates. 

Root Injury. — Most of the crops grown in humid regions that 
require cultivation are shallow rooting. A large supply of moisture 
and plant food is in the surface soil. The roots naturalh'' develop 
23 



354 



SOIL PHYSICS AND MANAGEMENT 



there in larger numbers, attracted by the favorable conditions for 
obtaining food and moisture. An examination will show many of 
the roots of cultivated plants within the surface three inches of 




Fig. 170. — Yields of corn (field weight) with different methods of tillage. (1911) 

soil under favorable conditions and probably three-fourths of the 
roots of the plants within the surface or plowed soil. 




Fig. 171. — Yield of com (field weight) with different methods of tillage. 

To preserve these roots from injury very shallow cultivation 
must be i^racticed. Eoots take nourishment from the soil for the 
plant and if roots are cut off it lessens the food supply. Kot only 
this, but it takes energy from the plant to reproduce the roots de- 



TILLAGE 



355 



stroyed. Experiments have been made with corn to show the effect 
of cutting the roots similar to what is done in cultivation to a 
depth of four inches. The following table gives the results obtained : 

Eesults of Shallow and Deep Cultivation and Root Pruning of Corn^ {Yields in 
Bushels Per Acre) 



Kind of cultivation 


1888 


1889 


1890 


1891 


1892 


189.3 


1896 


Average 

for years 

given 


1. None — weeds kept down by 

scraping with a hoe * . . . . 

2. Shallow — 4 or 5 times 

3. Deep — 4 or 5 times 

4. Shallow — roots unpruned . . . 

5. Shallow — roots pi-uned f. . . . 

6. Scraped with how * 


90.0 
93.8 
84.9 
97.0 
91.0 
94.0 

85.5 


77.1 

84.6 
74.2 
90.9 

78.3 
85.8 

68.4 


69.1 
66.8 
60.8 
78.7 
55.0 
76.7 

61.5 


55.3 
58.4 
63.4 
70.0 

48.7 
66.3 

39.7 


76.8 
70.1 
80.1 

78.9 
70.7 


28.7 
36.3 
33.6 
33.4 

26.2 


87.0 
85.5 
83.4 


67.7 
70.8 
68.6 
74.8 
61.6 
80.7 


7. Scraped with hoe,* roots 
pruned f 








68.3 





* No mulch produced. 

t A frame one foot square was placed over the hill of corn and a knife was run around 
the outside 4 inches deep. 

The effect of cutting the corn roots is shown by comparing plots 
4 and 5, where a difference of 13.2 bushels per acre is shown in 
favor of no root injury, and the difference is about the same when 
plots 6 and 7 are compared. 

Level Cultivation. — Under practically all conditions of rainfall 
and soils almost level cultivation is most desirable. Eido-ed cultiva- 




FiG. 172. — Level cultivation. 



356 



SOIL PHYSICS AND MANAGEMENT 



tion must necessarily be deep, and is always accompanied by root 
injury. In some alluvial bottom land ridging may be necessary. 
Where the annual morning glory or other troublesome weeds are 
thick deep cultivation may be advisable to cover them, especially 



■i '1- 



i^s^^ffmm^^^^^^^^'^^.f^' 




Fig. 173. — Ridged cultivation with drilled corn. A verj undesirable method with nearly 

all soils. 

if the corn is drilled and not checked. This forms a very strong 
objection to drilling corn. The ridge formed is sometimes six to 
eight inches high. The disk cultivator or the little diamond plow- 
are both used for ridging. The ideal cultivation is not absolutely 
level, but such as to have a slope of one to two inches between rows. 
Compare figure 172 and figure 173. 



QUESTIONS 

1. What was Jetliro TuU's theory of plant nutrition? 

2. Define tillage. 

3. Why is loosening the soil necessary? 

4. Give results obtained for plowing and not plowing. 

5. What are the advantages of turning under vegetable matter? 

6. Give advantages of killing weeds. 

7. Give tillage for storing and conserving moisture. 

8. Why is compacting necessary? 

9. Give action of mold-board plow in turning soil. 

10. What conditions are necessary for best pulverization? 

11. WTiat is the advantage of the stubble plow? 

12. What is the objection to using it in plowing sod? 

13. Describe the general purpose plow. 

14. Describe the sod plow and its work. 



TILLAGE 357 

15. What is the hillside plow? 

16. What are the advantages of the disk plow? 

17. What is the use of the lister? 

18. Describe the subsoil plow and give its use. 

19. Give points of difference in the kinds of harrows. 

20. What are the advantages of the disk harrow that make it so uni- 

versally used ? 

21. Why is it necessary to use compacters ? 

22. What are the objections to the drum roller? 

23. Give advantages of other forms of roller. 

24. What is a planker and for what used ? 

25. Describe the Campbell subsurface packer. 

26. What are its advantages ? 

27. Give three classes of cultivators. 

28. Give advantages and disadvantages of each. 

29. Which is best adapted to shallow cultivation? 

30. Give value of different seeders as tillage implements, 

31. Give four points in good plowing. 

32. What determines the time of plowing? 

33. What can you say about fall plowing? 

34. May the soil become too dry to plow in the fall? 

35. Give advantages of fall plowing. 

36. What soils are most benefited by fall plowing? 

37. What are some advantages of spring plowing? 

38. What preparation should be made for spring plowing? 

39. How deep should plowing be done ? 

40. What can be said of extremely deep plowing in humid regions? 

41. Tell about the results from subsoiling. 

42. What may be said in favor of dynamiting? 

43. What is the effect of deep rooting crops? 

44. \^Tiat are the advantages of a good seed bed ? . 

45. What are the objections to clods? 

46. Give the facts in regard to a good seed bed for wheat. 

47. What are the conclusions from the table page 347 ? 

48. How should the seed bed be prepared for corn from fall-plowed land i' 

49. Give method of preparing seed from spring-plowed land. 

50. Tell about seed bed for oats. 

51. What are the objects to be attained in the cultivation of a crop? 

52. Give results of weeds on yield of corn at the Illinois Station. 

53. What is the value of the mulch in growing corn as sho^vn by crop 

yields? 

54. Give results of the Department of Agriculture on cultivation of corn. 

55. What effect does root injury by cultivators have on yield of corn ? 

REFERENCES 

^Mosier, J. G., and Gustafson, A. F., Bulletin 181, Illinois Station, Soil 

Moisture and Tillage for Corn, 1915, p. 585. 
^ Call. L. E., Bulletin 185, Kansas Station, Preparing Land for Wheat, 

1913, p. 6. 
^Illinois Bulletin 181 (as above), p. 570. 
* Illinois Bulletin 181 (as above), p. 582. 
^'Cates, J. S., and Cox, H. R,, Bulletin 257, Bureau of Plant Industry, 

U. S. D. A., The Weed Factor in the Cultivation of Corn, 1912. 
^Morrow, G. W., Results given in Illinois Bulletin 181 (as above) p. 568. 



CHAPTEE XXVII 



SOIL EROSION 



Erosion is the removal of soil material by air or water in 
motion. The work of water alone will be cousidered in this chapter. 
The National Conservation Commission ^ states that " on the basis 
of estimates received from 30,000 farmers, representing, every 
county in the United States, 10,622,000 acres of farm land have 
been abandoned, and that 3,888,000 acres, or 0.2 per cent, have been 
devastated by soil erosion.^' Large areas in the states from Penn- 
sylvania to Georgia and westward, including Kentucky, Tennessee, 
Alabama, Missouri, Arkansas, Louisiana, and Mississippi, are sub- 
ject to serious damage by erosion. Even such prairie states as Illi- 
nois and Iowa suffer loss in this way. As an average of the sixty- 
one -counties of Illinois, of which a detailed soil survey has been 
made, it has been found by actual measurement of the soil areas 
that about 17 per cent is hilly and subject to serious erosion. 

Cause of Erosion. — Erosion occurs whenever rain falls on un- 
protected sloping land so rapidly or in such quantities that the soil 
cannot absorb the water as fast as it falls. The same is true of the 
melting snow. Only that water lost from the surface — the run-off — 
causes erosion. The run-off depends on (1) the slope or topography 
of the land, (2) the texture and structure of the soil, (3) the vege- 
tative covering, and (4) the character of the precipitation. 

1. Effect of Topography. — The run-off from mountain to- 
pography is from one-third to three-fourths of the total annual 
rainfall when it varies from 15 to 40 inches. Xewell estimates the 
run-off from the basin of the Savannah river to be 48.9 per cent 
(eight-year average) of the annual rainfall; 56.5 per cent from the 
Connecticut valley (13-year average), and 53 per cent (six-year 
average) from the Potomac basin. Greenleaf places the loss from 
the broad level to undulating basin of the Illinois river at 24 per 
cent, and Leverett ^ gives 21 per cent as the amount of run-off from 
Illinois as a whole. The run-off of the United States as a whole is 
estimated at one-third of the annual rainfall. 

2. Texture and Structure of the Soil. — Coarse soils absorb 
a much larger proportion of the rainfall than do the fine-grained 
ones. The rate of absorption depends on the size of pores, not on 

358 



SOIL EROSION 



359 



the total pore space in the soil. This fact explains the rapid ab- 
sorption by the coarse-grained soils and the slow action of the fine- 
grained ones. However, if the latter are loose and open from 
recent tillage their absorption compares favorably with that of 
coarser soils. Unless the finest-grained soils (clay loams and clays) 
are exceptionally well supplied with organic matter and limestone 
the beating of raindrops breaks down the grannies, diminishing the 
size of the pores, thus rendering the soil less absorbent. As a result 
a large amount of water is lost from even moderate slopes. 

3. Vegetative Covering. — ^The surface soil of a natural forest 
is usually covered with leaves and twigs, which protect it from 




Fig. 



174. — Two hundred square miles of once forested mountains in China, which a cen- 
tury ago paid rich revenue on their lumber product. (Bailey Willis.) 



erosion. It suffers little so long as this natural protection remains 
undisturbed (Fig. 174). Natural prairies are usually protected in 
this way by a good sod of native grass. The rain drops do not 
usually strike the soil direct and thus destroy the granules, as they 
tend to do in cultivated fields. When this covering which nature 
provided is removed or destroyed erosion takes place. 

4. Character o£ the Rainfall. — A gentle rain will be absorbed 
entirely by almost all soils, since it does not come more rapidly than 
the water can percolate through the soil, thus preventing complete 
saturation of the surface. A heavy rain falling on medium- or fine- 
grained soils soon saturates the surface and then absorption by the 
soil cannot take place any faster than percolation from the surface 
into the lower strata. 

Results of Erosion. — It is quite impossible to determine with 



360 



SOIL PHYSICS AND MANAGEMENT'. 



aiiy degree of accuracy the total quantity of material moved by 
water, but it must be many times as much as is deposited from sus- 
pension in lakes and the seas. 

Some geologists hold that the land surface of the earth as a 
whole is being lowered by erosion one foot in six thousand years. 
The combined loss from surface erosion and from solution by 
ground waters amounts to one foot in about 4100 years. 

AYhen a stream emerging from a narrow valley spreads out over 
the bottom land, the velocity of the water is checked and its load 
of stones, gravel and sand is deposited on the rich alluvial land. In 
this way much valuable soil is buried completely by material of little 
immediate use to plants. The finer material, if unweathered and 
deficient in organic matter, may be almost equally worthless until 
acted upon by the regular soil-forming agencies. If the deposition 
is rapid there is little chance for soil to form, but if deposition is 
prevented for a time this almost worthless material becomes a valu- 
able soil. 

1. Removal of Organic Matter and Nitrogen. — The surface 
soil contains the greater part of the organic matter, and so is the 
richest, most productive part of the soil. The removal of any ap- 
preciable amount of this stratum reduces the amount of plant food, 
especially the nitrogen, rendering the soil less productive than 
formerly. The following results from pot culture tests in the green- 
house show their great need of nitrogen : 





YieMs from Eroded Hill Lands ^ (Bus 


hcls 


per Aae) 




Treatment 


Pulasld 
county 
wheat 


Henry county 
oats 


None 


8 

9 

9 

69 


21 


Potassium 


23 




31 


Nitrogen . . 


225 







2. Changes Physical Character of Soil. — The removal of the 
surface soil exposes the yellowish or reddish subsoil, which is heavier 
and more difficult to work than the original surface soil. These 
exposures of subsoil are locally known as "clay points." They are 
less productive than the original land. In some residual and glacial 
soils with a wide range in size of particles the texture of the sur- 
face may he changed from a fairly heavy to a sandy or gravelly 
soil by the removal of the silt and clay, leaving only the coarse mate- 
rial which was too large to be carried away by the water. 



SOIL EROSION 361 

3. Changes of Color. — Erosion almost invariably results in a 
change of color of the soil. If the soil is brown, yellow or grayish 
yellow, erosion produces a yellow or reddish color, depending wholly 
on the color of the subsoil. On the Piedmont Plateau and some 
other residual soil areas the color becomes very red, due to exposure 
of the subsoil. 

' KINDS OF EROSION 

Two somewhat distinct types of erosion are recognized, sheet 
erosion and gullying. 

I. Sheet Erosion 

Water flowing over a uniform slope removes approximately the 
same amount of soil material from all parts. Sheet erosion is the 
source of far greater loss than gullying. The latter quickly and 
comj)letely ruins small areas, but the former reduces the produc- 
tiveness over large areas to the point of unprofitable returns. 

Methods of Prevention and Reclamation. — 1. Application 
cf Limestone. — Limestone in time renders the soil more porous 




Fig. 175. — Sweet clover on badly eroded land. Seeded in March, photographed in 

September. 

by producing granules. This lessens erosion, because the soil is 
more al)sorbent and the heavier compound granules are more diffi- 



362 SOIL PHYSICS ANP MANAGEMKNT 

cult to move tJian the individual particles. The more important 
effect of limestone, however, lies in its jnnver of eonvoting acidity, 
rendering the soil more favorable for the growth of legumes which 
furnish organic matter and nitrogen (Fig. IT.')), also for soil-bind- 
ing crops, such as timothy and bluegrass. 

2. Protection by Crops. — The surface of rolling land should 
be kept covered with soil-binding crops as much of the time as 
possible. Por this purpose meadows, pastures and catch and cover 
crops are indispensable in the farming of rolling lands. ^ 

(a) Meoilotts and l^asiures. — The perennial grasses, timothy in 
the northern states and red top and Bermuda grass further south, on 
acid soils are good meadow grasses. Bermuda grass makes good 
pasture and, if cut early enough, fairly good hay. Its growth is 
such as to stop washing very well. It is more protitable to gnnv one 
or more legumes with the grasses, as the latter use nitrogen fixed 
by the legume. This is particularly desirable on those soils deficient 
in nitrogen. Together these [dauts form a good sod, which prottvts 
the surface and holds the soil together. 

Much of these hilly lands should never be plowed, but kept in 
pasture. Bine grass, timothy, red top and other grasses, together 
with red, alsike and white clover, sweet clover {}fel{Iotus alba), and 
Japan clover {Lespedeza striaia), may be seeded in addition to 
native grasses that follow upon the removal of the forest. One or 
more of these should be able to get a good foothold regardless of 
whether the soil is acid or contains limestone. These legumes 
enable the grasses to make a much better sod. As already pointed 
out. legumes in general require a soil containing limestone for good 
growth. Japan clover, however, seems to be indifferent. Sweet 
clover is more successful than any of the other clovers under very 
unfavorable conditions if its two requirements — thorough inocula- 
tion and abundance of limestone — are satisfied. It makes a strong 
growth and may be pastured or grown for hay and seed. Blue grass 
soon starts in it, living in part on nitrogen fixed by the legumes. 
This increases the amount of pasture afforded and forms a better 
protection for the soil. 

(b) Catch and Cover Crops. — Cultivated land should not be 
left unprotected throughout the winter and spring months, especially 
in those sections where the soil is not frozen during any consider- 
able part of the winter. Cowpeas or soybeans may be seeded be- 
tween the rows of corn at the last cultivation or between the trees 
in orchards. Hairy or winter vetch and Japan clover are more 



SOIL EROSION 363 

desirable in some places, especially the vetch, as it lives through 
the winter and begiiis growth early in the spring. With fall sown 
cereals sweet clover may be used to good advantage when the soil 
is well supplied with plant food. Wheat, rye and winter oats cover 
the ground well and the roots are a very effective soil binder. Vetch 
and Japan clover are probably most desirable when sufficient growth 
is made, because of their ability to gather nitrogen, the increase of 
which is most essential in the improvement of these soils. Crab 
grass is a natural cover in seasons of normal rainfall, as it makes 
sufficient growth to serve well as a surface protection, especially in 
corn and old wheat fields. 

3. Residues. — Stalks of corn or cotton may be harrowed or 
rolled down after the crop is harvested. In this way they help to 
protect the soil from the beating of rain drops and reduce some- 
what the amount of thawing in winter and early spring. When the 
isurface soil is thawed for an inch or two, it is easily eroded. 

It is desirable, also, to cover badly eroded areas, or areas where 
erosion is especially rapid, with straw of grain or clover, manure, 
or other coarse material. These areas are unusually low in organic 
matter, as more or less of the surface soil has been removed. The 
coarse organic matter will not only hold tlie soil in place, but supply 
. plant food to succeeding crops. 

4. Increasing the Organic Matter. — Most lands subject to 
serious erosion have been timbered and are naturally low in organic 
matter and nitrogen. The hilly timber lands of Illinois contain 
an average of 1.5 per cent or 15 tons of organic matter in the sur- 
face soil (two million pounds per acre). The yellow silt loam — hilly 
timber land — of Hardin County,* Illinois, which represents the 
unglaciated loess-covered section of the states adjoining the lower 
Ohio and the middle section of the Mississippi river, contains as an 
average of 15 analyses 1.1 per cent or 11 tons of organic matter in 
the surface soil. The hill soils of the Piedmont Plateau, Appa- 
lachian Mountain Plateau, and Limestone Valleys and Upland 
Provinces contain from one-half to two and one-half per cent of 
organic matter.'' The average organic-matter content is about 1.4 
per cent.° Profitable crops cannot be produced without adding 
considerable organic matter or nitrogen. 

Besides furnishing nitrogen, organic matter aids granulation 
and cements the finer particles together into compound granules, 
as discussed under organic matter. These soils need the addition of 
large quantities of organic matter to enable the surface to absorb 



364 



SOIL PHYSICS AND MANAGEMENT 



and retain more of the rainfall. Owing to its granulating effect 
organic matter reduces the tendency to run together and keeps the 
soil open, so there is less run-ofE and less erosion. 

Legumes must have a large place in the agriculture of these 
lands. It is advisable to feed most crops to stock on the farm. All 
the manure produced should be carefully preserved and returned to 
the soil. All stalks, straw, stubble or other residues not fed should 
be plowed under. Plowing under the entire crop of cowpeas, or at 
least the straw, is a practice to be recommended. 

5. Deep Contour Plowing. — A loose soil has more pore space 
than a compact one, consequently it will absorb more water. A 





Fig. 176. — Cultivated terraces in China. (Bailey Willis.) 

silt loam in loose open condition will absorb 10 to 15 per cent more 
water than when compact. The pores in a compact soil are so small 
that it absorbs rain very slowly and much of the water is lost as 
run-off. The surface soil may be kept loose by plowing to a de|)th 
of eight to ten inches. Eight inches of loose silt loam fairly well 
supplied with organic matter is capable of absorbing two inches of 
water. While a greater depth of plowing would increase the storage 
capacity, experiments show such to be unprofitable. The Georgia 
Station '^ reports results which indicate that plowing more than 
eight inches deep lessens the yield of cotton. It is believed, how- 
ever, that loessial soils may be plowed to a greater depth with profit. 
Plowing on sloping land is best done across the slope with a 



SOIL EROSION 



365 



reversible or hillside plow, by which all of the soil may be turned 
in the same direction. In ordinary plowing up and down the hill 
the small depressions, nearly always found between furrows, and 
especially the dead furrows, serve as places where the water col- 
lects and erosion begins. In contour plowing these ordinary de- 
pressions are at right angles to the slope and retard rather than 
encourage erosion. When the reversible plow is used there are no 
dead furrows except on 'the crest of ridges where there is but little 
danger of erosion. 

6. Contour Seeding. — Corn and cotton should be planted on 
contour lines or nearly so. This reduces the danger of erosion in 
planter tracks, and the cultivation will be across the slope, which 
will avoid the formation of small gullies between the rows. For 
this reason the seeding of oats, wheat and cowpeas should be across 
the slope, particularly when the drill is used. 

7. Terraces. — In those sections where intensive farming is prac- 
ticed and in fruit districts where the rain falls in heavy showers and 
the soil does not absorb water readily, terracing is practiced to good 
advantage (Fig. 176). Three types of terraces are in common use — 
the guide row, the level bench and the Mangum. 

(a) The Guide Row (Fig. 177) is made by throwing four fur- 
rows together on contour lines, with an interval of approximately 




Fig. 177. — Guide-row terraces. There is no slope from one end of a terrace to the other, 
but there is a slight slope from the back of a terrace to the front. (Pearce, R. B.) 

three feet in altitude between the rows. This makes a low flat ridge, 
and in order to avoid any waste of land a row of the crop may be 
planted on it. This method of terracing is employed on slopes that 
do not exceed 10 per cent, or one foot in ten, and where the soil 
is open, absorbing the rainfall readily. 



366 



SOIL PHYSICS AND MANAGEMENT 



(b) The Level Bench (Fig. 1T8) is employed on steeper slopes. 
These may be developed from the guide-row or laid out on contours 
by using a reversible plow. By plowing down hill a level bench is 
developed in a few years. "When the desired form of the terrace 
has been produced it is well to throw the soil up the slope as often as 
down in order to avoid exposing too much unproductive subsoil at 
the upper side of the terrace. Each bench must be cultivated as a 
separate unit, and driving over the bank or outer edge must be 
avoided lest depressions be made which result in gullies. The 
growth of weeds on the edge of the bench should be prevented and 




Fig. 178. — Level-bench terrace. (Bui. 2.36, North Carolina Station.) (F. R. Baker.; 



a good grass covering encouraged to prevent erosion. Crops may be 
grown in straight rows or on contours following the terrace lines. 
Most farmers object to the short rows^ which are necessary if the 
rows are to be kept straight, because of the loss of time and the 
tramping out of part of the crop in turning during cultivation. 
Undoubtedly the best way to prevent erosion while farming these 
lands is to plant and cultivate across the slope or parallel to the 
terrace. The uncultivated bank growing weeds or grass is a serious 
objection to this form, as it is a breeding place for injurious insects 
and a home for moles, mice and other animals. Very often the 
water from the slope above finds its way into one of their burrows 
and a considerable gully forms in a short time. A terraced park 
is shown in figure 179. 

(c) The Mangum Terrace (Fig. 180) is a very desirable form, 
because it eliminates the uncultivated spaces of the level bench. It 



SOIL EROSION 



367 




Fig. 179. — A terraced park in Mississippi. While the natural slope was stable under the 
protection of the ^drgin forest, it was necessary to terrace to prevent devastating erosion 
when the land was cleared. (Bureau of Soils, U. S. D. A., Bui. 71.) 




Fig ISO --The Mangum terrace 



Dept of -^gr ) 



368 



SOIL PHYSICS AND MANAGEMENT 



differs from the guide row and level bench in that the lines are not 
level, but are run across the slope with a grade of six to ten inches 
in 100 feet towards some natural outlet into which the water may 
drain. The terrace is made by plowing several furrows along the 



n 




Fig 181 — Locusts growing on gullied land. The gullies have been almost completely 

filled. (Heaton.) 

surveyed line and pulling the soil to the lower side so as to form 
a low dyke or ridge with a shallow depression just above it. The 
crop is planted obliquely over the dyke and terrace, so that water 
may collect along the rows and be conducted into this depression, 



SOIL EROSION 369 

or wide bottomed ditch, wliicli has but slight fall, so there will be 
little or no erosion. The Mangum terrace can be used to good ad- 
vantage on heavy soils which absorb water very slowly. This form 
provides very effective protection against erosion and eliminates 
waste land. 

8. Reforesting. — As already pointed out, the soil of virgin for- 
ests is protected by leaves and twigs. On cleared areas where the 
surface soil has been removed to such an extent that it does not 
produce profitable crops and especially where gullied it may be 
advisable to imitate nature by planting trees. The black locust is 
excellent for this purpose. Being a legume it is capable of good 
growth on soils very low in organic matter. The leaves and twigs 
protect the soil and, through the aid of nitrogen fixed by the legume, 
grasses soon start among the trees (Fig. 181) . By this time there is 
little movement of soil material. T\^ien abandoned, such areas are 
reforested naturally, but the process is very slow and much ad- 
ditional erosion may take place before there has been sufficient 
growth to hold the soil. The natural growth in most cases will be 
of far less value than the black locust or other trees which might be 
selected for this purpose. 

9. Tiling. — In rolling sections, "seepy" or "springy" spots 
are common. On these, crops do poorly, wheat often " heaves " and 
may be killed completely. In wet seasons these spots are much 
larger than normal, so the damage is much greater. In many of 
these places and on much rolling land which does not have an 
especially pervious subsoil, tile will produce all its ordinary bene- 
fits, including warmer, drier surface soil in the spring when early 
tillage and planting are desirable. The most beneficial effect of 
tiling is the increase in perviousness of the soil, so that the rains 
are absorbed more readily, thus decreasing the run-off. This is a 
very effective method of preventing erosion, but the expense is al- 
most prohibitive when that is the only purpose to be accomplished. 

II. Gullying 

In any depression extending up and down a slope water col- 
lects. Its velocity is increased with its volume, as is also its trans- 
porting and eroding power. For this reason depressions extend- 
ing down the slope, such as a furrow, wagon or planter track, a 
sheep or cow path, or even a mole tunnel, may soon result in a small 
gully. These should be filled with some coarse organic matter or 
24 



370 



SOIL PHYSICS AND MANAGEMENT 



obliterated in other ways-. Otherwise, each rain will increase their 
size and they will become a permanent source of trouble. In a 
few years considerable areas will be ruined. Gullying in different 
degrees is seen in figures 182, 183, and 184. 

Methods of Prevention and Filling. — 1. Straw-brush. — 

Fig. 182. 






Fig. 183. 

Fig. 182. — Erosion in pasture near crest of slope. 

Fig. 183. — Old field erosion in Mississippi. 

Gullies should be filled with a durable material sufficiently open 
to allow the water to pass through it and yet reduce the velocity of 
the current so as to cause deposition. The material best suited 
depends on conditions. If the slope is gentle and the quantity of 
water small, straw, weeds, or anything of that nature holds the soil, 
that would otherwise be lost, partially filling the gully. Where the 



SOIL EROSION 



371 



slope is steeper or the amount of water greater, steps must be taken 
to prevent the rapidly flowing water from washing away the mate- 
rial used. For this purpose stakes slanting up hill, driven through 
the straw are used successfully. Hedge or other brush (Fig. 185) 
placed on the straw help to hold it. Stones may well be used for 
this purpose, especially if they occur on adjoining slopes. 

Stock frequently make paths up and down steep slopes to such 
an extent that the grass is killed and a slight depression produced. 
Water collects in this during rains and a gully is started. 

In pasture lands, waterfalls sometimes occur that move up the 




Fig. Isl. — Old erosion. 

slope by means of headwater erosion (Fig. 186). As water goes 
over the fall it undermines the sod surface, which then caves in, 
making a gully which is especially difficult to fill. In such places 
it is necessary to protect the face of the bank from the undermining 
action of the water. This may be done by filling the gully at the 
fall with brush or straw or both, which must be held in. place by 
stakes or heavy material, such as stones. Since the water from 
pasture land contains but little sediment, filling of gullies under 
these conditions is a very slow process. For completely filling the 
gully, dams of some kind must be used below the fall. 

2. Dams. — In cultivated fields earth and concrete dams are 
used for filling large gullies. The earth dam is built over a large tile 



372 



SOIL PHYSICS AND MANAGEMENT 

Fig. 185. 




Fig. 186. 
Fig. 185. — Brush checking erosion. 
Fig. 186. — Headwater erosion. 




Fig. 187. — Earth dam for checking erosion. 



SOIL EROSION 



373 



laid in the gully to be filled. A vertical tile connects with the 
horizontal one a few feet above the dam. This form of dam is 
adapted to comparatively small gullies of slight fall which do not 
carry large amounts of water. 

The dam holds the soil material carried down by the stream 
and the water which would otherwise overflow the dam and ruin it 
passes down through the vertical tile and out through the horizontal 
one. The arrangement of the tile is shoAvn in figure 187. 

Concreie dams are better adapted to large gullies carrying a 




Fig. 188. — Filling a gully by means of a concrete dam. 

large volume of water. They should be placed well into the bed 
of the gully and extended into the bank well back from the gully 
(Fig. 188). The concrete should be thoroughly reinforced. A spill- 
way with an ample concrete floor below the dam is absolutely nec- 
essary to prevent the water which passes over from undermining 
it. The vertical tile is sometimes used as with the earth dam, but 
it is not so essential, but the horizontal tile should be used for 
draining the temporary pond above the dam. 



374 SOIL PHYSICS AND MANAGEMENT 

3. Vegetation. — Among the many plants that may be used to 
excellent advantage in checking the deepening and widening of 
gullies, the black locust is probably the most valuable tree. Gullied 
soils are always low in nitrogen, yet the locust thrives in spite of 
this fact. The roots help to hold the soil and the leaves and twigs 
also ojffer some protection. The locust adds some nitrogen to the 
soil and grasses soon get a footing, which then catches the finer 
material. The gully may be almost entirely filled in this way. 
Locust trees are valuable for posts if not attacked by borers. Wil- 
lows and cottonwoods and a few other trees may be used in the 
same way, but their wood is of less value and few, if any, of them 
possess the advantages of the locust. (See Fig. 181, page 368.) 

Timothy, blue-grass, redtop, sweet clover, Japan and other 
clovers are very useful in all gullies, but more especially in wide, 
flat-bottomed ones where erosion is not so severe as to prevent 
them from getting a good start. 

In many localities the sod of blue-grass or timothy in draws is not 
disturbed when the field is plowed for corn. ^Vllere limestone is 
applied or where its roots can reach carbonates in the subsoil sweet 
clover is exceptionally valuable because of its strong, rapid growth. 
On the steep limestone slopes of Kentucky sweet clover has reclaimed 
large areas of abandoned land which now produce excellent pasture 
and large crops of seed. 

4. Filling with Soil. — On more gently sloping land gullies 
may be filled with soil by means of plows and scrapers. This 
method can be employed with profit only on those areas where 
more or less intensive agriculture is to be practiced or where filling 
a few small gullies in this way will reclaim considerable areas. 
Much subsoil will be on the surface which will be very unproductive. 
Legumes must be gi'own for supplying organic matter and nitrogen, 
thus restoring fertility. If the soil is acid cowpeas is the best crop 
to grow. If the soil contains limestone or if limestone is applied 
sweet clover is one of the best legumes for the soil, as it grows under 
very adverse conditions. Whichever crop is grown should be re- 
turned to the soil. Figure 175, page 362, shows sweet clover grown 
under the above conditions. 

QUESTIONS 

1. How much land has been abandoned in the United States? 

2. What percentage in Illinois is hilly ? 

3. How do other states compare with Illinois in this respect? 

4. Upon what does run-off depend? 



SOIL EROSION 375 

5. Give effects of topography. 

6. What part does texture of soil play in erosion? 

7. How does the vegetative covering affect erosion ? 

8. Why should the character of rainfall affect erosion? 

9. Give some idea of the amount of material moved by running water. 

10. What is the effect of this deposit in many instances ? 

11. Give effects of removal of surface soil. 

12. What results are obtained from applying plant food to eroded soil? 

13. What effect does erosion have on the physical character of the soil? 

14. Define sheet erosion. 

15. HoAv does it reduce productiveness ? 

16. What benefits are derived from limestone on eroded land? 

17. Wliat are good meadow- and pasture-grasses? 

18. What are good legumes for hill land pastures? 

19. What are the uses of catch crops? 

20. What use may be made of crop residues? 

21. Tell about the amount of organic matter in eroded soils. 

22. What effect does it have that causes less erosion? 

23. What are the advantages of deep plowing? 

24. What are the advantages of contour plowing and seeding ? 

25. What is the guide-row terrace and what are its advantages? 

26. Give advantages of the level bench terrace. 

27. Describe the Mangum terrace. 

28. Give its advantages. 

29. Discuss reforesting of eroded lands. 

30. What about tile as a method for preventing erosion? 

31. What are the sources of gullies? 

32. Give methods of preventing gullies. 

33. Discuss waterfalls. Why are they so difficult to check? 

34. How may dams be used to fill gullies? 

35. Give use of black locust on gullied land. 

36. What other ways of filling gullies? 

REFERENCES 

^Report of the National Conservation Commission (60th Congress, Second 
Session, Senate Document 676), 1909, vol. 1, p. 79. 

== Leverett, F., Monograph XXXVIII, U. S. Geol. Survey. 

^Hosier, J. G., Circular 119, Illinois Station, Washing of Soils and Methods 
of Prevention (Second Edition), 1912, p. 7. 

* Soil Report No. 3, Illinois Station, 1912, p. 3. 

^ These figures are drawn from Field Operations of the Bureau of Soils, 
U. S. D. A., 5th Report, 1903. The average figure is based on reported 
analyses of 63 samples of the clay, clay loams, silt loams and loams 
of the Cecil, DeKalb, Hagerstown, and Norfolk Series. 

« Redding, R. J., Cotton Culture, Bulletin 63, Georgia Station, 1903, p. 124. 

General References. — ^McGee, W. J., Bulletin 71, Bureau of Soils, 
U. S. D. A., 1911. Ames, C. T., Bulletins 108 and 165, Mississippi Station, 
Report of Work at the Holly Springs Branch Station, 1907-1914. Illinois 
Soil Reports, No. 3, 1912, and No. 11, 1915. Davis, R. 0. E., Bulletin 180, 
U. S. Department of Agriculture, Soil Erosion in the South, 1915. Calhoun, 
F. H. H., Circular 20, South Carolina Station, Gullying and its Prevention, 
1913. 



CHAPTEE XXYIII 



ROTATION 



A CKOP rotation is the growing of two or more crops in regular 
sequence on the same land. Scientific rotation is the S3'stematic 
growing of crops on the same soil in regular succession such that 
each crop bears a useful and somewhat vital relation to some or all 
of the others grown. Eotation is very closely related to and be- 
comes the basis of soil improvement. The object of a rotation is to 
utilize, to the very best advantage in the production of maximum 
crops, the favorable conditions of soil with respect to tilth, moist- 
ure, temperature and food, produced by other crops, and to elimi- 
nate any unfavorable conditions produced by any crop. A legume 
should form one of the crops of the rotation because of its value in 
bringing about these favorable soil conditions. 

Major crops in rotations are the main crops grown. Minor crops 
are those grown for catch, cover, or green manure purposes. 

In nature no very distinct rotation of plants occurs because 
the same thing is accomplished in a measure by the growing to- 
gether of different plants on the same land. Yet we see that nature 
has its own system of rotation. Certain plants may grow luxuri- 
antly for a few years and then be almost entirely replaced by some 
more favored one. Sweet clover has been observed growing along 
ditch banks for several years and then has been crowded out by some 
other plant without any apparent cause. As a result of weather 
conditions some weeds are very abundant for a year or two and 
then almost entirely disappear. Fires sometimes aid nature in 
bringing about a rotation of plants, as do also birds and other 
animals. Any natural agency of seed distribution lends its assist- 
ance in accomplishing this purpose. 

In agricultural practice it has been found very essential to 
rotate crops. The object of farming is to grow crops and it has 
been found in general farm practice and determined through num- 
erous experiments that more grain and other crojos may be produced 
in a regular rotation than by growing any one crop year after year 
on the same land. 
376 



ROTATION 377 

ADVANTAGES OF ROTATION 

1. Better Distribution of Work. — The one-crop system throws 
a large amount of work at about the same time so that a large 
force of men and horses are necessary to plant, cultivate or harvest 
the crop. The most economical use of time and labor is accom- 
plished when it is more uniformly distributed throughout the year. 
In a rotation the several crops are planted at different times. They 
mature so as to distribute the work of harvesting over a considerable 
period. This helps solve the farmer's labor problems by furnishing 
more permanent employment to the laborer. 

2. Control of Insects and Plant Diseases. — A very serious 
objection to any one-crop system is the encouragement it gives to 
injurious insects that prey upon the crop. This is especially true 
of corn. The corn root aphis and the corn root worm become very 
serious pests where this crop is grown very long in succession. 
Growing some other crop for several years destroys many of these. 
The same is true of plant diseases such as flax wilt, cowpea wilt, 
clover sickness,, potato scab, dry rot of corn, etc. These are worse 
than the insects. They may be completely controlled by rotation, 
since in this case the particular host plant upon which each lives 
will not be present every year, thus creating conditions very un- 
favorable for their survival. 

3. Control of Weeds.— Many crops have their particular weed 
or weeds that are in some way favored by them. Many weeds 
favored by one crop will be smothered by another. Cultivation 
of one crop may be the means of destroying some, while others may 
be killed by pasturing or by a tough, heavy sod. 

One-crop systems tend to encourage many kinds of weeds. At 
Eothamsted, England, on the plots where wheat had been grown 
continuously for many years the ground became so foul that fallow- 
ing had to be practiced occasionally to eradicate the weeds. Corn 
cockle and chess growing with wheat are familiar examples in this 
country. Eemove these from their association with wheat and they 
are easily killed. Old pastures sometimes become so full of weeds 
that the grass amounts to little. Ox-eye daisy, yarrow, verbena, and 
iron weed sometimes take pastures. Hence it becomes as necessary 
to rotate pastures as any other crop unless great care is taken to 
keep these enemies out. Pastures and meadows may be kept clean, 
as seen in England, where the grass fields are several decades old'. 



oTS SOIL PHYSICS AND MANAGEMENT 

These are the exceptions. EngUmd's farms are models of scientific 
rotation. 

4. Variation in Depth of Root Systems. — By rotation ditfer- 
ent crops with root systems vavviug iu depth are brought sncces- 
sively upon the hmd. Some especially deep-rooting crops, sneh as 
clovers and alfalfa, should be grown. These obtain ninch of their 
food below the zone from which the ordinary shallow-rooting crops 
take their food. ^More than this, they bring mnch plant food to 
where it may be reached by other crops. In this way the plant food 
from a deeper zone is utilized and soil exhaustion will not occur so 
soon. These deep-rooting crops have a very favorable effect in open- 
ing up the subsoil for better aeration and drainage. 

5. Helps Maintain Good Tilth. — At the University of Illinois 
one plot has been growing corn for thirty-seven years ; another has 
had a two-crop system of corn and oats : a third has had a three-crop 
system of corn, oats, and clover for the same time. The soil of the 
first is compact, "nms together" badly, and erodes considerably. 
A heavy rain packs it and forms a smooth, solid surface. The second 
acts somewhat similarly to the first but is not so bad. . The third is 
mellow, granular, and even hea\y rains do not cause the surface to 
run together. This difference is due to the legume crop growm. 
Xo crop is of more benefit to the tilth of a soil than a deep-rooting 
legume. 

6. Helps to Maintain the Organic Matter. — The part rota- 
tion plays in maintaining organic matter has been discussed in 
Chapter XI. As previously shown, a legume crop is essential iu 
every scientific rotation. The manner in which the legimie is dis- 
posed of is of the utmost importance. Yery little in the way of 
permanent improvement is accomplished unless the legume is turned 
back into the soil either directly or as manure. 

7. Rendering Toxic Substances Less Harmful. — Soils some- 
times contain organic substances that are harmful to plants. The 
same substance is not equally injurious to all crops, but is espe- 
cially detrimental to the growth of the kind of plants that gave rise 
to the toxic material. Changing the crop renders this less harmful. 

8. Produces Larger Yields. — From what ha^ been said it will 
be seen that rotated crops have a decided advantage over those of 
the single-crop system. 

!Many experiments have been carried on at different stations 

that prove definitely the great value of rotation in increased yields. 

Iowa gives results that show a nine-year average for continuous 



ROTATION 



379 



corn of 51 bushels per acTe and 64 bushels for corn grown in a 
rotation of corn, corn, oats, and clover. 



Rotation Compared with Continuous Com. 


Ames, Iowa 






1904 


1905 


1906 


1907 


1908 


1909 


1910 


1911 


1912 


Average 


Corn in rotation of 
corn, corn, oats 
and clover 

Continuous corn .... 


75 

74 


87 
73 


69 
53 


57 
47 


70 
53 


54 
31 


60 
46 


44 
32 


60 

47 


64 
51 



It will be observed that the yield at the beginning was about the 
same for each. 

At the Illinois Station corn has been grown for thirty-seven 
years in comparison with a corn and oats and a corn, oats, and 
clover rotation. The last four crops of corresponding years average : 
Continuous corn 26.4 bushels per acre, corn and oats rotation 34.6 
bushels, and the corn, oats, and clover rotation 57.1 bushels. 

Yields of Corn, Wheat and Hay Under Different Systems of Cropping. 
Minnesota Station '■ 







Corn 




Wheat 


Hay 


Year 


Con- 
tinu- 
ous 


3-year 
rota- 
tion 


5-year 
rota- 
tion 


Con- 
tinu- 
ous 


3-year 
rota- 
tion 


5-year 
rota- 
tion 


3-year 
rota- 
tion 


5-year 
rota- 
tion 


1899 


Bushels 

20.8 
37.5 

13.9 

* 

23.6 
11.1 
25.1 
27.6 
23.6 


Bushels 

51.1 

42.6 
42.0 
62.0 
54.7 
45.1 
64.1 
36.1 
35.2 


Bushels 

31.3 

58.0 
42.8 
78.6 
85.3 
37.1 
64.4 
60.5 
52.2 


Bushels 

22.5 
14.5 
16.0 
17.0 
16.3 
20.8 
20.8 
14.1 
24.5 


Bushels 

25.3 
27.3 
13.5 
18.1 
24.4 
27.3 
20.6 
13.3 
19.1 


Bushels 

27.3 
25.6 
1.5.2 
25.1 
30.8 
32.0 
30.9 
22.6 
23.9 


Tons 
L58 

2.25 
3.86 
4.26 
4.86 
1.91 
1.25 


Tons 


1900 




1901 

1902 


2.36 
1.95 

6.10 

5.77 
5 81 


1903 

1904 


1905 


1906 


3 18 


1907 


1.42 


Average, 9 years 

Increase 


22.9t 


48.1 
25.2 


56.7 
33.8 


18.5 


21.0 

2.4 


25.9 

7.4 


2.85t 


3.80t 
.95 



* Record lost. 



t 8 years. 



t 7 years. 



From the results given in the above table it will be seen that con- 
tinuous cropping has a greater effect on corn than upon wheat. The 
3-year rotation increased corn 25.2 bushels, while the increase for 
wheat was only 2.4 bushels per acre. 

Ohio has been carrying on some experiments for about 19 years 
that prove the value of rotations. 



380 



SOIL PHYSICS AND MANAGEMENT 



Average Annual Yields for 16 to 19 Years When Grown Continuously and 
Under Three- and Five-year Rotations. Ohio Station ^ 



Corn 



Wheat 



Oats 



Clover 



Continuous 

3-year rotation 

5-year rotation 

Increase for 3-year rotation 



Bushels 

15.88 
34.39 
29.74 
18.51 



Bushels 

7.52 

10.63 

10.21 

3.11 



Bushels 
22.92 



31.00 

8.08 



Founds 



2,697 
2,267 



Eotation gave an increase of 18.5 bushels per acre of corn and 
for wheat 3.1 bushels, showing again that corn responds to rotation 
better than wheat. 



PLANNING A ROTATION 

Planning a rotation requires a great deal of care and thought. 
It should be made not for the present alone but for many years in 
the future. The probable effect of the rotation adopted should be 
studied from several standpoints. The effect on the fertility and 
tilth of the soil should receive careful attention. Will it decrease 
or increase the organic matter of the soil is a question that should 
be worked out. If this rotation is practiced, what will be the condi- 
tion of my farm after fifty years? If you cannot answer this, get 
the knowledge or the help that will enable you to do so. The rota- 
tion would depend on the size of the farm to some extent. That 
for one of sixty acres would not apply to a four hundred-acre farm. 
The rotation should vary with the character of the soil. A rotation 
for a heavy, rich, black soil certainly would not be fitted for a sandy 
soil, or vice versa. Soils low in organic matter should have a system 
of rotation whose object is to build up the soil in this particular. 
Acid soils will grow different crops than soils containing limestone. 
The maintenance of the fertility and tilth of the soil should be a 
very important factor in determining the rotation. 

The system of farming to be practiced should be one of the con- 
trolling factors in determining the crops grown. A fruit-grower, 
a dairyman, a grain farmer, or a stock-raiser would each follow dif- 
ferent systems. In any system the value of the crops, both those to 
be used on the farm and those to be sold, must be considered in their 
selection, since the returns- from the crop and its relation to other 
crops is the thing that should determine its use in the rotation. 
The most profitable crop should have the most favorable place in the 
rotation. In the corn and wheat belt these should have this place, 



ROTATION 381 

and likewise of the other great money crops, such as cotton, tobacco, 
potatoes and others. 

As a general rule a rotation of three to five years is more desira- 
ble than a longer one. The short cycle requires less trouble and time 
to get it started and is easier to maintain when once under way. 
If a crop fails in a three- or four-year cycle it is not difficult to 
maintain the rotation, while if a failure occurs in a longer cycle it 
may disarrange the system to a greater or less extent. 

Because of the rearrangement of fields and the adjustment of 
crops, it is rather difficult to get a rotation under way, usually re- 
quiring several years, and it is almost equally difficult to change it 
after once it is started. The rotation should be maintained even 
if a crop does fail. A substitute crop should be planned to take the 
place of those crops that are liable to fail. This will not be needed 
very often. 

The farm should be divided into as many fields as there are 
years in the rotation and the crops grown in regular succession on 
these fields. On large farms the rotation may be duplicated. There 
should be at least one legume crop, preferably a biennial or peren- 
nial, and not more than two tilled crops, during the cycle, the 
number depending upon the soil, as these cause considerable loss of 
organic matter. 

Places in Rotations for Crops. — Corn succeeds well after 
clovers, alfalfa and pasture and does fairly well after wheat and 
oats, especially for fall plowing. In sod ground two or three crops 
of corn may be grown successfully, but more than two in succession 
on ordinary soil are not deemed best. 

Wheat does not follow corn well even if the latter matures sev- 
eral weeks before seeding time. Wheat does well after potatoes, 
clover, alfalfa, pasture or soybeans, the only danger being its liability 
to lodge caused by the excess of available plant food, especially 
nitrogen. Oats is a good crop to precede wheat if the plowing is 
done early. Wheat follows wheat very well, but there is too much 
danger from Hessian fly in some latitudes. 

Oats is a crop that is adapted to the cooler part of the temperate 
zone. South of this the ordinary spring-sown oats encounter the 
hot weather at filling time, so that a partial failure may result. In 
the South winter oats are groT\Ti to some extent with fair success. 
There is a belt between these where neither fall nor spring oats 
do well. The summers are too hot for the spring seeding and the 
winters too cold for the fall oats. 



382 SOIL PHYSICS AND MANAGEMENT 

In the corn and wheat belt and corresponding latitudes oats are 
almost universally seeded after corn. Even in the southern states 
this is practiced. If they should follow clover or potatoes, lodging of 
the crop would almost certainly occur, with consequent loss. They 
will follow wheat, millet or cotton well. 

Barley does well in the southern oats belt and under practically 
the same conditions. It may follow wheat, oats or corn. 

Eye may be grown under practically the same climatic conditions 
as wheat, but it is a better forager and produces more on poorer 
soils. In the middle west it is a common crop for very sandy lands. 

The clovers are almost universally seeded with wheat, oats or 
barley as nurse crops. Occasionally they may be seeded in corn or 
cotton after the last cultivation, but the catch is uncertain. 

Soybeans and cowpeas follow almost any crop, but there is noth- 
ing gained by having these succeed other legume crops. A non- 
leguminous crop should intervene or at least be grown in conjunc- 
tion with one of the legumes. 



SOME PRACTICAL ROTATIONS 

1. For the Corn and Winter Wheat Belt. — In this belt corn 
and wheat are the money crops, and they should be given the most 
favorable places in the rotation. If any crop is grown that is of 
special benefit to the soil, these should have the advantage of its 
effect. The best place for corn is following the legume. If two 
important money crops are placed in the rotation, each should be 
given the best place possible. This belt is characterized by hot 
summers and cold winters, with the annual rainfall varying from 
20 to 48 inches. Corn, wheat, oats, and rye are the principal 
cereals (Fig. 189). 

A short-cycle rotation that is sometimes practiced is : first year, 
corn; second year, oats, seeded to clover; and third year, clover. 
This is a good rotation to maintain organic matter, but it is not as 
profitable as some others. 

An excellent four-year rotation is made by adding another year 
of corn to the. former, making (1) corn; (2) corn; (3) oats 
(clover) ; and (4) clover. This exhausts the soil more rapidly than 
the former and is best adapted to fertile soils well supplied with or- 
ganic matter. If it is desired to grow wheat, a four-year rotation 
is as follows: (1) corn, (2) oats, (3) wheat (clover), (4) clover. 
This is well adapted to a rich soil such as black clay loam or a 



ROTATION 



383 




384 Both PHYSICS AND MANAGEMENT 

heavy phase of brown silt loam. If two croj)s of wheat are desired 
in the rotation, the extra one may follow the clover, seeded again to 
a different kind of clover to be jjlowed under for corn. This changes 
it to a five-year cycle. Another practical one where wheat is the 
leading crop is (1) wheat; (3) wheat (clover) ; and (3) clover. 

Probably one of the best four-j^ear rotations for the corn belt 
and one which gives two good money cro|)s advantageously located 
in the cycle is (1) corn, (2) oats (clover), (3) clover; (4) wheat 
(clover). This gives three years during which the legume crops 
are growing and the rotation is adapted to soils deficient in nitrogen 
and low in organic matter. On the grain farm practically all of 
the clover crop should be turned back into the soil in any of these 
rotations. The clover may be clipped and left on the land and the 
second crop may be harvested for seed and the straw returned to the 
soil. All crop residues not fed should' be turned back into the soil. 
If more corn is desired this may be changed to a five-year rotation 
by adding another year of corn, making (1) corn, (2) corn, (3) 
oats (clover), (4) clover, and (5) wheat (clover). 

These rotations are well adapted to either grain or mixed farm- 
ing, since the clover may be pastured to good advantage. Another 
year of pasture or hay may be easily added by seeding clover and 
timothy instead of clover alone. The first year of these the crop will 
be largely clover, while the second will be mostly timothy. If the 
clover should fail, soybeans may be substituted to be cut for hay or 
seed. Soybean straw is eaten very readily by stock. 

If soybeans or cowpeas can be used to good advantage, a rotation 
containing one of the crops may well be practiced. The rotation 
might be (1) corn, (2) cowpeas or soybeans, (3) wheat (clover), 
(4) clover. The cowpea or soybean hay may be fed' to stock and 
the manure returned to the soil. 

Alfalfa may be included in the rotation by adding another field 
and growing it while the other crops are going the rounds of the 
regular rotation. At the end of this cycle, the alfalfa field is then 
put into corn and the clover field is seeded to alfalfa. 

In these rotations alsike, mammoth, medium red, or sweet clover 
may be used. Where conditions are very favorable for getting a 
catch of alfalfa, this crop may be substituted for clover, but as a 
general rule it is a wise plan to leave a good stand of alfalfa for 
several years when once obtained. 

2. For the Cotton Belt, — This region p"ossesses many advan- 
tages in climate over the corn belt. It has a larger and better dis- 



ROTATION 385 

tributed rainfall with a longer growing season and mild winters. 
The unusual facilities for growing a money and a soil renovating 
crop during the same season give this section decided advantages 
over the corn belt. Winter cover crops on rolling land for prevent- 
ing erosion, as well as green manure crops for increasing the scanty 
supply of organic matter, should be grov^^n more extensively. 

The principal money crop is cotton, yet a great many special 
crops are grown in different states. Mixed farming predominates 
in many places. In Kentucky, Tennessee, and Oklahoma livestock 
farming prevails, with the growing of grains next in importance. In 
Texas and Arkansas livestock is first, with cotton production second. 
Cotton is the leading crop, in Alabama, Mississippi, Georgia, South 
Carolina, and Louisiana. In the latter, sugar cane is next in im- 
portance. This is also grown in North and South Carolina. 
Tobacco is grown extensively in Maryland, Virginia, Kentucky and 
North Carolina. Truck crops and fruits are extensively grown in 
Florida and near the Gulf in other states. Corn, rice, wheat, oats, 
kafir corn, milo maize, rye and buckwheat are grown in different 
parts of the region. 

The forage crops are varied and comprise alfalfa, cowpeas, soy- 
beans, red, alsike, crimson, Japan, and sweet clovers, vetches, 
timothy, blue, Johnson, brome, and Bermuda grasses, and millet. 
Peanuts, hemp, Irish and sweet potatoes are special crops in some 
sections. 

This shows the large number of crops that are grown in this belt 
and the great opportunity for rotation. Much of the soil is acid 
and deficient in organic matter and nitrogen, and the rotation- 
should be planned to maintain or increase the nitrogen rather than 
attempt to supply it from commercial fertilizers. Legumes must 
be grown that are not affected by acid unless limestone or lime has 
been applied to the soil. Japan clover, cowpeas, and soybeans fill 
these conditions, since they do very well on acid soils. 

The cotton belt includes a very extensive area, large numbers 
of widely different soils, and considerable variation in altitude. 
These tend to give variety to the crops grown. The rotation for this 
belt should have one or more money crops, such as potatoes, cotton, 
tobacco, sugar cane, wheat, rice, one or more for feed and a crop 
for soil improvement. A very good rotation is (1) corn (cowpeas), 
(2) winter oats (cowpeas), (3) cotton (clover). 

Where tobacco is grown, the following may be practiced: (1) 
tobacco, (2) wheat (clover), and (3) clover; or (1) corn (cowpeas), 
25 



386 SOIL PHYSICS AND MANAGEMENT 

(2) tobacco, (3) wheat (clover) and (4) clover. In the rice 
district the following is recommended: (1) rice, (2) rice, (3) corn 
(cowpeas), (4) winter oats (cowpeas), or (4) winter oats and 
vetch (cowpeas). 

If one of the money crops is potatoes, then (1) corn (cow- 
peas), (2) potatoes (soybeans), and (3) cotton (crimson clover) 
may form the rotation. Th'e legumes in corn and cotton should 
be used primarily for soil improvement, while those following other 
crops may be used for hay or soil improvement. These rotations 
are only suggestive. For the stock farm, almost any of the above 
rotations may be extended two or three years for hay or pasture, or 
both, with whatever meadow or pasture grass does best in the 
locality, whether it is redtop, timothy, brome, blue, or Bermuda 
grass. 

3. For Hay and Pasture Province. — The hay and pasture 
province (Fig. 189) occupies the northeastern part of the United 
States in the cooler temperate zone with a southward extension 
in the Appalachian Mountains to northern Georgia. Grass for hay 
and pasture is the principal crop grown, yet corn, potatoes, rye, 
oats, wheat, clover, and barley are somewhat extensively produced 
in many areas. 

The short seasons do not permit the growing of two crops and 
hence the greater difficulty of raising soil-renovating crops. There 
is, however, this advantage, that oxidation of organic matter does 
not takei place so rapidly as in warmer climates and the supply is 
therefore easier to maintain. 

The following rotations are recommended: (1) Potatoes, (2) 
rye (clover), (3) clover; or (1) corn, (2) potatoes, (3) rye 
(clover), (4) clover. For pasture or hay timothy may be seeded 
with the clover and left for two or three years. If desirable, oats 
may be substituted for rye. If potatoes are omitted, a good rotation 
is as follows: (1) corn, (2) oats, (3) wheat (clover), (4) clover 
and timothy, (5) timothy. This rotation may be shortened by 
leaving out wheat, making a very desirable rotation for some 
localities. 

4. The spring wheat region and the great plains province 
occur east of the Rocky Mountains, and wheat is the principal crop 
of both. In the former (1) corn, (2) wheat, (3) wheat, and (4) 
legume may be practiced. In some localities potatoes may be sub- 
stituted for corn. In a live stock system, clover and timothy may 
be sown and used for hay and pasture. 



ROTATION 387 

The crops of the great plains province vary extensively. Besides 
wlieat, the sorghums form a very valuable crop in the southern 
third. To the north of this, wheat, together with some corn and 
alfalfa, is the principal crop. No definite rotation has been worked 
out for this area. 

The principal farm crops in the provinces west of the Eocky 
Mountains are wheat and alfalfa, with some corn, oats, barley, rye, 
and sugar beets. The need of soil improvement is not so evident 
here as in humid regions, because of a much greater original sup- 
ply of plant food. The extensive growth of alfalfa furnishes a 
ready and effective means for building up the soil, 

QUESTIONS 

1. Define a rotation of crops. 

2. How does a scientific rotation difier from the above? 

3. Give the objects of a rotation. 

4. What are major crops ? 

5. What are minor crops ? 

6. HoAv are crops rotated in nature? 

7. Wliat is the primary object of farming? 

8. How does rotation aft'ect the distribution of work? 

9. Wliy is a one-crop system favorable to the development of insects? 

10. Can you give an instance of disease caused by continuous cropping? 

11. How does rotation prevent disease? 

12. How are weeds kept down by rotation? 

13. Give some examples of troublesome weeds in your locality that may be 

kept down by rotation. 

14. Why is it a good practice to grow crops that root at different 

depths ? 

15. What part does rotation play in maintaining tilth? 

16. What are toxic substances and how does rotation affect these? 

17. Give the results obtained at the Iowa Station for continuous corn 

and rotation. 

18. What results were obtained at the Illinois Station? 

19. What do the Minnesota experiments show in regard to corn? Wheat? 

Hay? 

20. Which cereal responds best to rotation? 

21. If corn is Avorth 50 cents and wheat $1.05 per bushel and hay $8 per 

ton, what is the total value of the average crops in a three-year 
rotation ? In a five-year rotation ? 

22. Which rotation gave the greatest acre value for the crop? (Assume 

that in a five-year rotation, three crops of hay were grown.) 

23. Give a synopsis of the Ohio results. 

24. What things are to be considered in planning a rotation? 

25. What importance should be placed on the soil in these plans? 

26. Wliat consideration should guide in the selection of crops? 

27. What determines the succession of crops? 

28. \^Tiat about the length of the rotation? 

29. Why is it difficult to get a rotation under way ? 

30. Why is it advisable "to divide the farm into as many fields as there 

are crops in the rotation? 



388 SOIL PHYSICS AND MANAGEMENT 

31. Where should corn be placed in the rotation? 

32. Where is the best place for wheat? 

33. Where are oats grown best ? 

34. Where are winter oats grown? 

35. What crops may well be followed bjj oats? 

36. Where may rye be seeded ? 

37. What is a nurse crop and why necessary? 

38. What do cowpeas and soybeans follow? 

39. Locate the corn and winter wheat belt. 

40. What are the principal crops there ? 

41. Give a good short-cycle rotation. 

42. Give a good four-year rotation. 

43. What is the rotation if two crops of wheat are desired? 

44. Give a four-year rotation in which legumes are grown three out of 

four years. 

45. How may these be adapted to mixed farming? 

46. What is to be done if clover should fail ? 

47. What is the place of soybeans or cowpeas in the rotation ? 

48. How may' alfalfa be included in the rotation? 

49. Locate the cotton belt. 

50. What advantages over the corn and winter wheat belt does it possess? 

51. What are the principal money crops? 

52. Name some other crops grown in this belt. 

53. Give the forage crops grown. 

54. Give a practical rotation with tobacco, cotton, rice and potatoes. 

55. What should be done with the legumes? 

56. How may these be adapted to livestock farming? 

57. Where is the hay and pastvire province? 

58. What are its advantages and disadvantages? 

59. Give rotations that may be practiced. 

60. Locate the spring wheat region. 

61. Name the crops and give a rotation. 

62. What are the crops of the great plains region? 

63. What are the important crops of the province west of the Eocky 

Mountains? 

REFERENCES 

^Hays, W. M., Boss, Andrew, Wilson, A. D., and Cooper, Thomas P., 

Bulletin 125, Minnesota Station, 1912, p. 36. 
=* Circular 131, Ohio Station. 

General References. — Carleton, M. A., Small Grains, 1916. Liv- 
ingston, George, Field Crop Production, 1915. Montgomery, E. G., Pro- 
ductive Farm Crops, 1915. Piper, C. V., Forage Plants, 1914. Duggar, 
J. F., Southern Field Crops, 1915. Parker, E. C, Field Management and 
Crop Rotation, 1915. 



APPENDIX I 

: SOIL FERTILITY 

Without attempting to go into the subject of soil fertility to 
any great extent, the authors have thought that a brief discussion 
of the subject, giving some of the underlying principles, would be 
helpful to the farmer. The field is such a large one, and the theories 
advanced are so varied and conflicting, that the practical farmer 
is at a loss to know what to do, and as a consequence does nothing. 
The fertility needs of soils may be determined in three ways: (1) 
by chemical analysis, by which the amount of plant food may be 
determined, (2) by pot culture experiments in greenhouses under 
almost perfect conditions, and (3) by actual field tests, where plant 
foods of different kinds may be applied and the results compared 
with those of an equal area of the untreated soil growing the same 
crop. 

Permanent Agriculture. — Agriculture is usually considered a 
permanent industry, but it is no more permanent than the natural 
soil itself. If the fertility of the natural soil is inexhaustible, then 
agriculture is a fixed industry and likewise those industries, com- 
merce, manufacturing, and mining, which depend so largely upon 
agriculture. If history tells us anything about agriculture it is 
this : that it is not permanent, that nations have fallen because the 
agriculture upon which their civilization depended had failed. 

Are Soils Inexhaustible ? — ^The productiveness of soils depends 
upon the amounts and kinds of plant food elements they contain, 
the favorable conditions for plant growth that they offer, and the 
friendly bacteria present. Chemical analyses show that plants 
contain certain mineral elements which they obtain from the soil. 
Analyses show further that soils contain these elements in limited 
quantities, and it requires no great amount of mathematical knowl- 
edge to see that if plants take even small amounts of these elements 
from this limited supply, reduction and final exhaustion are sure 
to follow unless the necessary elements are added by the farmer. 

Complete exhaustion of plant food is not necessary to render a 
soil unproductive. If the soil presents adverse conditions to the 
plant, either through lack or excess of water, poor aeration, or bad 
physical condition, or if the proper bacteria are not present, or, 

389 



390 



SOIL PHYSICS AND MANAGEMENT 



being present, are not under favorable conditions for carrying on 
their work, the plant suffers and the soil appears as if exhausted. 

Plant Food Elements. — Ten elements are essential to the 
growth of plants. (See the table on page 3.) Of these, sulphur, 
calcium, magnesium, iron, nitrogen, phosphorus, and potassium are 
furnished by the soil. The 1-ast three are the ones most liable to be 



Plant Food in Crops 



Crop 



Kind 



[Amount 



Nitro- 


Phos- 


Potas- 


Mag- 


gen 


phorus 


sium 


nesium 


Poundi 


Pounds 


Pounds 


Pounds 


71 


12 


13 


4 


25 


4 


45 


4 


100 


17 


19 


7 


48 


6 


52 


10 


2 




2 




38.1 


8.3 


11.2 


2.6 


25 


6.5 


35 


3.5 


66 


11 


16 


4 


31 


5 


52 


7 


42 


7.9 


10.1 


2.9 


15.6 


2.3 


23.7 


1.8 


7 


o 


3 


1 


160 


20 


120 


31 


3. 


0.4 


4 




63 


11 


19 




102- 


18 


59 




80 


13 


24 


2.1 


79 


8 


49 




130 


14 


98 




72 


3.5 


90 


11.7 


118.4 


3.5 


118.4 


0.9 


72 


9 


71 


2.4 


300 


27 


144 


22.8 


100 


18 


157 


72 


63 


13 


90 


5.4 


75.1 


12 


111 


54 


16 


2 • 


18.4 


11.2 


25 


7 


1 




57 


7 


12 





Cal- 
cium 



Wheat l^^"^ 

^'^^^^ \ straw 

f grain 

Corn \ stover 

I cobs 

^y' Sw 

oats kZ 

B»*y (£?aw 

/^i J seed 

Clover ■••Uay 

lint 

Cotton j seed 

I stalk 

o L / seed 

Soybeans jg^j.^^ 

Cowpea hay 

Tobacco jg^t^ii^ 

Timothy hay 

Alfalfa hay 

Sugar beets 

Potatoes 

Turnip-roots 

Turnip-leaves 

Fat cattle 

Milk 



50 bushels 
2}4 tons 
100 bushels 

3 tons 
3/9 ton 

40 bushels 

23^ tons 

100 bushels 

2}yi tons 

50 bushels 

2600 pounds 

4 bushels 
4 tons 

1000 pounds 

2000 pounds 

4000 pounds 

25 bushels 

2.25 tons 

3 tons 

1800 pounds 

3200 pounds 

3 tons 

6 tons 

20 tons 

300 bushels 

15 tons 

2 tons 

1000 pounds 

10000 pounds 



Pounds 
1 

10 

1 

21 



0.9 
11.0 

2 
15 

1.0 

6.0 

1 
117 



1.7 



67.5 

28.4 

7.2 

218.4 

64 

3.6 
183 
109.2 



* Compiled from various sources. 

deficient in soils. There are many indications, however, that cal- 
cium may become so low that legumes, which require large amounts 
of it. may suffer in their growth because of an insufficient supply. 

Removal of Plant Food. — Crop Requirements. — Eemoval of 
plant food from the soil by the crop is one of the common causes 



SOIL FERTILITY 391 

of lessened production. From the table on page 390, which gives 
the amount of plant food used by some common crops, it will be 
seen that a fifty-bushel crop of wheat requires ninety-six pounds of 
nitrogen, sixteen of phosphorus, fifty-eight of potassium, eight of 
magnesium, and eleven of calcium, a total of only one hundred and 
seventy-nine pounds. This is only two and one-fourth per cent of 
the weight of grain and straw produced. The percentage of plant 
food taken from the soil is the same for corn, while for oats it is 
slightly more than two and one-half per cent. For the crop to 
obtain even this small amount, it is necessary that much larger 
amounts be present in the soil, since only a small proportion is 
available each season. The yields given in the preceding table are 
high, but no larger than rich soils will produce under favorable' 
conditions. 

The legumes take most of their nitrogen from the air, but the 
other elements given in the table are taken from the soil. Other 
crops take all of their supply of these elements from the soil. Be- 
sides the elements given in the preceding table, iron is taken from 
the soil. However, there is such an abundance of iron in the soil 
and plants require so little that soils probably will never become 
deficient. In the case of sulphur, the amount needed is small and 
the soil receives some from the air during rains. 

Supply of Plant Food in Soils. — The supply of plant food de- 
pends upon several factors. Probably the most important is.tbe- 
rock from which the soil was derived. A soil derived from a sand- 
stone may contain very little plant food of any kind. A granitic / 
soil will probably contain large amounts of calcium, potassium, / 
some magnesium, and phosphorus. A limestone soil would contain 
considerable amounts of each element. Soils formed by mixtures 
of various rocks usually contain the largest supply. 
/ Mtrogen is nearly always a later acquisition. Very few rocks, \^ 
Sc,as.that term is commonly used, contain nitrogen. ' 

/ Leaching removes large amounts of plant food, and for this 

reason the soils of humid regions contain less than those of arid 
ones. Some exceptions occur in swamps, where the mineral plant 
food has been carried in by washing and leaching from the higher 
areas. Conditions are favorable for the accumulation of nitrogen 
through the more luxuriant gro'«i;h and less rapid oxidation of vege- 
tation. The physical composition of the soil plays a very important 
part in leaching, since the smaller the soil particles the less the 
leaching. 



592 



SOIL PHYSICS AXD MANAGEMENT 



The cropping to -vrhich the soil has been subjected determines 
to a large extent the plant-food content. Every crop removed from 
the land takes awav a certain amount of food, thus slowlv reducinof 
the supply. 

The next table gives the amount of plant food in soils from 
various countries. 

Total Plant Food in Some Residual Soils* — Pounds in Two Million Founds 

of Soil 



^ , . Phos- Potas- -, , . Mag- 

bulphur phorus sium ; Calcium i nesium 



Mar\-land barrens 

Adobe soil. New Mexico 5200 

Coral Hmestone. Bermuda Islands . 

Soil from gneiss 1380 

Soil from gabbro 740 

Serpentine soil 560 

Cambrian sandstone soil SOO 

Trenton limestone soil S20 



2000 
28600 

2000 
22200 
15400 
27600 
57400 
51600 



580 
19SS00 
50200 
5600 
7S00 
S200 
9000 
8200 



840 
35600 
5800 
7000 
10600 
39000 
14S0O 
10400 



* Compiled from various sources. 

Fertility in Eu^ian Steppe or Tchernozem Soils} — Pounds in Two Million 

Pounds of Soil 





Xitrogen 


Sulphur 


Phos- 
phorus 


Potas- 
sium 


Caldum 


Mag- 
nesium 


Virsdn 


5100 

4S0O 


560 

640 


1220 
1133 


11950 
S630 


21562 
1S700 


8800 


Cultivated 


9000 



Plant Food in Missouri Soils.- — Pounds in Two Million Pounds of Soil 



Soil 




The standard of a ver>' fertile soil 

Northeast Missouri level prairie i \'andalia) . . 
Northeast Missouri level prairie (High Hi ll) . . 
Northeast Missouri rolling prairie ( Hurdlandi 
Northeast Missouri rolling prairie (Fulton.. . 

North Missouri timber soil (.Laclede) 

Ozark upland (Climax Springs) 

Ozark upland (Otterville) 

Ozark upland i Stonehill) 

Ozark border (New Haven) 

Ozark border (Wittenberg) . - . - 

West Missouri rolling prairie (Garden City). . 
Southeast Missouri lowland silt (Hajid) 
Southeast Missouri lowland sandv soil (Camp- 
beU) 



6000 2000 



2700 
3760 
3640 
3000 
1180 
1820 
1620 
1460 
1500 
3560 
5320 

1700 



1608 

1978 

1754 

1221 

800 

1350 

740 

740 

1660 

1445 

4584 

1711 



4714 
6089 
7188 
5362 
2889 
4117 
2623 
5495 
5429 
5262 
17785^ 

3566 



son. I'ERTILITY 



:v.rA 



Plant Food in tSoil Areas of Kentucky.^ — Pouiuh in Hurjace, to 7 Inches, 
Two Million Founds 



Formation 

Trenton 

Cincinniitiiin 

Hiluriun and Devonian 

Waverly 

St. Louis 

Chester 

Western coal field 

Eastern coal fi(ild (western part.) 

Eastern coal field (central and eastern part) 

Quaternary 

River alluvium 



Total 
nitrogen 



37S0 

;iiso 

24X0 
I%0 
21()() 
1700 
I !),S0 
2H0 

'z\)m 

VMi) 



Total 
phosphori 



94 Ki 
1924 
1100 

or^o 

890 
702 
7()(i 
(i-'JO 

1200 
9S0 

1910 



Total 
potuHijium 

2()278 

:n900 

2:5940 
19000 

2S22() 

2(irj(io 

29290 
ISISO 

;{42];i 

:5092() 

;j44;i0 



By taking the figures of crop requirements given in the tables, 
pages 390 and 398, it will be easy to calculate the Iciigih ot 
time necessary to completely exhaust the soils by growing maximum 
crops. This will give a fair idea of the deficiency of certain plant 
foods in the soil. 

Nitrogen. — Nitrogen is one of the most limited of the plant 
food elements in soils. It occurs in organic matter in combination 
with hydrogen, oxygen, carbon, sulphur, and other elements, and 
all non-leguminous plants are indirectly dependent upon this form. 
Legumes also use the nitrogen of the organic matter. Free nitrogen 
occurs in the soil air in large quantities, but this can be used only 
by legumes. One hundred corn crops of fifty bushels each would\ 
use all the nitrogen in the surface soil of the average brown silt i 
loam, provided the stalks were turned back, while if the stalks and / 
grain were both removed the nitrogen would all be used in a littl<5 
more than sixty-five years. 

Through the activity of soil organisms the soil nitrogen of the 
organic matter is slowly made available. The process takes place 
principally in the plowed soil and the amount of nitrogen made 
available each season is approximately two per cent of the total 
nitrogen in this stratum. If there are four thousand pounds in 
the plowed soil, about eighty pounds will become available, or an 
amount sufficient to produce a fifty-bushel crop of corn. 

Nitrogen is the limiting element over large areas of soil, and 
i^ increase and maintenance becomf.s one of tHe moil important as 



X 



394 



SOIL PHYSICS AND MANAGEMENT 



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SOIL FERTILITY 



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SOIL PHYSICS AND MANAGEMENT 



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SOIL FERTILITY 



397 



well as one of the most difficult problems for the farmer (Figs. 190 
and 191), The methods that have been recommended for main- 
taining the organic matter will usually maintain the nitrogen. It 
is the most expensive plant food element, and more of it is required 
by crops than of the other elements. When the market price is 
eighteen cents per pound the cost of the nitrogen for a bushel of 
corn is twenty-seven cents, for wheat thirty-six cents, and for oats 
r, : . . . . fl ^ . l"^-^ 




Fig. I'JO. — iVheat growing on a s^il very deficient in nitrogen. Note the effect of the 
addition of nitrogen (N). Average yield for nitrogen, '62 grams per pot, without nitrogen 
3 grams. (Illinois Soil Report.) 




Fig. 191. — Legumes turned under have the same effect as the addition of nitrogen. 
Yields for a four-year average were as follows: No nitrogen, 4 grams per pot, legumes 18 
grams, and for nitrogen 20 grams. (Illinois Soil Report.) 

about eighteen cents. This price makes its purchase almost, if not 
entirely, prohibitive for ordinary grain crops. 

Nitrogen can be readily incorporated with the soil by turning 
under a crop of inoculated legumes. These may be grown in con- 
nection with some of the money crops, such as corn, cotton, wheat, 
rye, oats, and others, and turned under for soil enrichment. The 
cotton belt and the southern part of the corn and wheat belt are 



X 



398 



SOIL PHYSICS AND MANAGEMENT 



especially well adapted to this method. It must be remembered 
that nitrogen is readily lost by leaching, especially after it becomes 
available. 

It would be well to emphasize the necessity of turning the 
legumes under instead of removing them. In many places the 
legumes are made into hay and sold from the farm, or fed without 
returning the manure. Under these circumstances very little is 
accomplished toward permanent soil improvement by growing 
legumes. 

Composition of Tops and Roots. Crops Seeded July 22 {Delaware Station) 



Crop and date of harvest 


Air-dry 
matter 


Pounds per acre and 
per cent in roots 


Nitrogen 


Phos- 
' phorus 


Potas- 
sium 


Cowpeas, tops 


3718 

301 

9 


65.2 

4.2 

.1 


7.2 

1.0 

.1 


39.2 


Nov. 7, Roots to 8 inches 

Roots 8 to 12 inches 


1.9 
.1 






Per cent in roots 

Soybeans, tops 

Nov. 11, Roots to 8 inches 

Roots 8 to 12 inches 


8 

6790 

717 

39 


6.0 

130.9 

8.8 
.5 


13.0 

16.5 

1.0 

.0 


8.0 

38.3 

1.4 

.1 






Per cent in roots 


10 

3064 

584 

16 


6.5 

108.0 

12.8 
.4 


5.5 

9.8 

2.0 

.1 


4.0 


Vetch, tops 


65.1 


Roots to 8 inches 

Roots 8 to 12 inches 


5.7 
.2 


Per cent in roots 


17 

5372 

381 

32 


11.0 

128.2 

5.7 

.5 


18.0 

25.9 

.8 
.1 


8.0 


Crimson clover, tops 


69.7 


Nov. 20, Roots to 8 inches 

Roots 8 to 12 inches 


3.2 
.3 






Per cent of roots 


7 

2267 
1962 

8 


6.0 

54.8 

40.2 

.2 


3.5 

5.7 

3.7 

.0 


5.0 


Alfalfa, tops 


26.7 


Roots to 8 inches . . . . ' 

Roots 8 to 12 inches 


7.9 
.0 




47 

2819 
1185 

27 


42.0 

69.8 
32.5 

.7 


39.0 

8.3 

4.3 

.1 


23.0 


T?f>rl olnvpr tons 


38.6 


Nov 22 Roots to 8 inches 


8.0 


Roots 8 to 12 inches 


.2 






Per cent in roots 


30 


32.0 


35.0 


18.0 







SOIL FERTILITY 399 

From the preceding table it will be seen that of the legumes 
given, alfalfa adds the largest amount of nitrogen to the soil, forty- 
seven per cent in its roots, and red clover second with thirty -two 
per cent. When the two crops of red clover are removed from the 
land, the nitrogen left in the soil in roots and stubble is on an 
average probably no more than equal to that taken from the soil by 
the crop, so there is no addition of this element under such a prac- 
tice. The table shows that the roots of cowpeas, soybeans, and 
crimson clover contain a very low per cent of the total nitrogen. 
These crops if harvested from the land probably not only add no 
nitrogen but actually remiove some from the soil. 

Fresh farmyard manure contains about ten pounds of nitrogen 
per ton, and the futility of trying to maintain this element with 
manure on the average grain farm is readily seen. All manure 
should be used to the best advantage, but where fifty bushels of 
corn per acre, and other crops that remove equivalent amounts of 
nitrogen, are grown it would require about twenty tons of average 
farmyard manure per acre every four years to maintain it, even if 
there were no other source of loss. 

Commercial Forms of Nitrogen.— The forms in which 
nitrogen may be obtained commercially for use as a fertilizer are 
as follows : 

1. Sodium nitrate constitutes the principal form in which the 
element nitrogen is obtained for use in commercial fertilizers. The 
salt occurs in northern Chili and after being purified by crystalliza- 
tion contains 15 to 16 per cent of the element. Chlorides and sul- 
fates are present in small quantities. It is very readily soluble and 
should be applied only when the crop is growing to prevent loss 
by leaching, since it is not absorbed to a very great extent by the 
soil. It is used by market gardeners and may be applied to timothy 
meadow and small grains. Its continued use deflocculates the soil, 
producing a puddled condition. 

3. Ammonium Sulphate. — Ammonia is a by-product in the 
distillation of coal and the sulfate is produced by passing the am- 
monia through sulfuric acid. It contains about 20 per cent of 
nitrogen. This salt is readily absorbed and because of this is not 
so readily leached from the soil. It should not be applied in the 
fall, because it will be changed to nitrates and leached out and lost. 
Its continued use tends to deflocculate the soil somewhat as sodium, 
nitrate does. 



400 SOIL PHYSICS AND MANAGEMENT 

3. Cyanamid or Calcium Cyanamid. — This is an artificial 
product made by passing nitrogen into retorts containing highly- 
heated calcium carbide. It is a heavy, black, granular powder, and 
should be incorporated with the soil for some days before planting 
to avoid any toxic effect that might be injurious to the seeds and 
young plants. It contains about 16 per cent of nitrogen. 

4. Organic Substances. — Certain materials that were formerly 
waste products are valuable for their nitrogen. Among these are 
cottonseed meal, containing 7 or 8 per cent of nitrogen; linseed 
meal, with about 5.5 per cent; dried blood, containing from 13 to 
15 per cent, and tankage, which has from 4 to 10 per cent of 
nitrogen and 1 to 8 per cent of phosphorus. 

Phosphorus. — Large areas of land all over the world are 
deficient in the element phosphorus to such an extent that it be- 
comes the limiting factor. It is especially important in the pro- 
duction of grain and in the growth of legumes. Its addition helps 
to make possible the building up of soil by larger growth of nitrog- 
enous soil-renovating crops. In addition to this it improves the 
quality and increases the weight of the grain (Figs. 192 and 193). 

The needs of a soil for phosphorus may be determined by apply- 
ing two hundred and fifty pounds of steamed bone meal per acre to 
wheat or corn by sowing broadcast before the seed bed is prepared 
and securing accurate yields of equal areas of the treated and un- 
treated land. Definite conclusions, however, should not be based 
upon a single year's results. 

Phosphorus may be purchased in several forms: (1) raw bone 
meal, (2) steamed bone meal, (3) raw rock phosphate or floats, (4) 
acid phosphate, and (5) basic or Thomas slag. 

Bone meal is made from the bones of animals slaughtered at 
the packing houses. The bones are a by-product and their high con- 
tent of phosphorus makes them valuable. The raw bones may be 
ground up into meal, but this contains three to five per cent of 
nitrogen and large amounts of fat and oil. The nitrogen is very 
expensive, while the fat is of no value to the soil. The bones may be 
steamed under high pressure, thus removing the fats and oils and 
gelatin. The bones are then ground into meal that is placed on the 
market as steamed hone meal. This contains less nitrogen and more 
phosphorus than the raw bone. 

Rock Phosphate. — Phosphorus has been deposited in large 
quantities as a mineral combined with other elements forming the 
tri-calcium phosphate, practically the same as bone in composi- 



SOIL FERTILITY 



401 




Fig. 192. — Wheat, 1911, LVbana field. Cover crops and farm manure plowed under, 
age jrield, 34.2 bushels per acre. (Illinois Soil Reports.) 



Aver- 




FiG. 193. — Wheat, 1911, Urbana field. Cover crops and farm manure plowed under. 
Finely ground rock phosphate applied. Average yield, 51.8 bushels per acre. (Illinois Soil 
Reports.) 

26 



402 SOIL PHYSICS AND MANAGEMENT 

tion. Large deposits are found in South Carolina, Florida, Ten- 
nessee, Utah, and other states. This is mined and, when finely 
ground, constitutes the raw roch phosphate of commerce. When 
this phosphate is treated with an equal weight of sulfuric acid, the 
resulting product is acid phosphate. This treatment renders most 
of the phosphorus available. - It contains from six to eight per cent 
of the element phosphorus. 

Basic slag, a by-product formed in the manufacture of steel 
from iron ores containing considerable phosphorus, has been ex- 
tensively used in Europe as a source of phosphorus, but to no large 
extent in this country. 

Forms Compared. — Of these different sources, steamed bone 
meal, acid and raw rock phosphate are most commonly used. 

Without entering into a lengthy discussion of the merits of each 
of these, it may be said in general that upon soils low in organic 
matter acid phosphate or steamed bone meal may be used to good 
advantage. If the soil is well supplied with organic matter, finely 
ground rock phosphate will be preferable, since the acids produced 
by the decay of the organic matter render the phosphorus available. 
Any form of quickly decaying organic matter, such as legumes, green 
or barnyard manure, will aid in liberating the phosphorus. For im- 
mediate results the rock phosphate should be applied before the 
material is turned under. It may be added to the soil for the pur- 
pose of helping to obtain a catch of clover. For best results with any 
form of phosphate, limestone should be present in the soil. 

In the use of phosphorus on soils deficient in this element the 
one purpose should be to increase the amount by applying more 
than is used by the crops. A naturally fertile soil rarely contains 
less than fourteen hundred to sixteen hundred pounds of the ele- 
ment per acre in the plowed soil. 

Most upland soils, as shown by the tables on pages 392, 393, and 
394, actually contain from eight hundred to twelve hundred pounds. 
In the building up of these soils an excellent plan is to add a ton of 
finely ground rock phosphate per acre every four to six years until 
the amount has reached that of a normal fertile soil, or about 
eighteen hundred to two thousand pounds in the surface seven inches 
of an acre. After this is reached a sufficient amount should be 
applied to replace that removed by the crops. 

The cost of a pound of the element phosphorus is a thing that is 
frequently overlooked. In bone meal and acid phosphate the cost 
of a pound of phosphorus was about twelve and one-half cents per 



SOILS FERTILITY 403 

pound in 1916, while in the rock phosphate the phosphorus cost 
from two and one-half to three cents per pound, depending upon 
the distance from the mines, in material containing fourteen per 
cent of the element phosphorus or 33 per cent of phosphoric acid. 

If rock phosphate of the same money value as acid phosphate 
or bone meal were applied and the conditions were at all favorable, 
the results obtained would compare well with those from the other 
forms and the phosphorus content of the soil would be increased, 
as so much more of the element would be added. 

Potassium. — As may be seen from the tables, pages 392, 393, 
and 394, soils vary a great deal in their content of potassium. Clay -,7 
and silt soils contain the most, while peats and sands have least. - 
Many peat soils are so deficient in this element that applications of 
potassium are necessary. Notwithstanding the large amount in 
soils, it is sometimes so unavailable that crops fail to obtain the 
amount necessary for good yields. Potassium is usually locked up 
in silicate minerals and the action of acids of some kind is necessary 
to liberate it. This may be accomplished by the acids of decaying 
organic matter which attack the minerals and free the potassium. 

In soils such as peat the potassium may be supplied by applica- 
tions of potassium sulfate or chloride, each containing about eight 
hundred fifty pounds of the element per ton, or kainit, containing 
two hundred pounds (Fig. 194). Wood ashes contain five per cent 
of potassium. Annual applications of one hundred to two hundred 
pounds of the sulfate or chloride per acre are sufficient for most 
crops. Manure may be used, but a ton contains only eight pounds, 
and the nitrogen of manure has a much greater value upon other 
types of soil. 

Other Elements. — While several other elements are required 
for crops, the supply in the soil is so large, or the amount used by 
crops is so small, that there is little danger of a deficiency. Sul- 
fur is required in small amounts, and probably will need to be 
applied only in the case of crops such as turnips, cabbage, etc., which 
require large amounts. Iron is used only in small amounts and 
the soil contains an abundance. Calcium and magnesium are low 
in some soils, especially acid ones, and may be easily supplied in 
limestone, which has been discussed in Chapter XII. 

Lime, Limestone. — All soils should contain some carbonate, but 
more especially calcium carbonate or limestone. Its presence is 
very important in the functioning of nitrifying bacteria and the 
production of available nitrogen. A base must be present to unite ^ 
with the nitrous and nitric acids formed, or the presence of these 



404 



SOIL PHYSICS AND MANAGEMENT 



free acids will inhibit the action. Chemical combination takes 
place and calcium nitrites and nitrates are formed, the latter of 
which are available for the use of plants. 




Fig. 194. — Corn on peaty swamp land, 1903. Lime and phosphorus at top, yield 0. 
Lime and potassium at bottom, yield 72.5 bushels per acre. (Bulletin 157, Illinois Agri- 
cultural Experiment Station.) 

The element calcium is used by plants as food, as shown by the 
table on page 390, and there is little doubt but that it may be limit- 
ing the size of the crojDs on some soils. 

Soils frequently are acid or become so after long cropping, 
bringing about conditions unfavorable for the growth of many 
legumes. This acidity may be removed by the use of lime, lime- 
stone, or some other carbonate. Many bacteria cannot develop in 
an acid soil. 



SOIL FERTILITY 



405 



Lime and limestone have a beneficial effect upon the physical 
condition of the soil^ since it produces flocculation or granulation. 
This process is especially important upon heavy soils and those 
deficient in organic matter, and for this reason is more beneficial 
when applied to such soils. Quicklime is more effective in this way 
than calcium carbonate. , 

Nitrogen, Phosphorus and Potassium in Fertilizing Materials, Pounds Per 
Ton of 2000 Pounds 



Material 


Nitrogen 


Phosphorus * 


Potassium f 


Acid phosphate 


■ ■ ■ 400 ' " 


114 to 160 




Ammonium sulfate 




Apatite . . . 


300 to 400 

8 to 14 

8 to 18 

88 to 160 




Ashes, wood leached 




16 to 50 


Ashes, wood, unleached. . . . 




66 to 132 


Basic slag 






Blood, dried 


260 to 300 
60 to 80 
40 to 60 

140 to 160 




Bone meal, raw 


180 to 220 

200 to 220 

18 to 26 




Bone meal, steamed 




Cottonseed meal 


25 to 33 


Kainit 


200 to 220 


Linseed meal 


110 

10 

300 to 320 


15.6 
2 


22.6 


Manure, barnyard, fresh.. . 
Nitrate of soda 


8 


Phosphate : 

Tennessee rock 


240 to 300 
320 




Florida hard rock 




Potassium chloride 




820 to 880 


Potassium nitrate 


260 




730 


Potassium sulfate 




800 to 840 


Tankage, general range .... 
Tobacco waste 


80 to 200 
40 to 80 


20 to 160 

4 to 8 




80 to 160 







* To find the weight of phosphoric acid (P2O5) per ton multiply the weight of phos- 
phorus by 2.3. 

t To find the weight of potash (KjO) multiply the weight of potassium by 1.2. 

Forms in Which Lime May Be Applied. — Lime may be ap- 
plied to soils in several different forms. Quick or caustic lime may 
be used, but it is now generally believed that it is not the best form 
to apply because of its tendency to encourage the decomposition of 
organic matter. 

Air-slaked lime is a form that may be used, but its extreme fine- 
ness invites active solution and loss by leaching. 

Marl is formed by chemical precipitation in small lakes in glacial 
regions, and consists of a more or less impure calcium carbonate, 
usually somewhat loose and fine. It is only of local significance. 



406 SOIL PHYSICS AND MANAGEMENT 

Limestone when ground so that it will pass through a screen of 
ten meshes to the inch makes an excellent material for applying to 
the soil. The dust or finely ground limestone is ready for imme- 
diate use, while the coarser part gives durahility so that applica- 
tions will not need to be made so often. 

The Best Form to Apply.- — Experiments have been carried on 
at some experiment stations to test the value of different forms. At 
the Pennsylvania Station two tons of slaked lime once in four years 
and of ground limestone every two years were used on different plots 
and the total yields were greater for ground limestone. Analyses 
of samples from each plot showed 375 pounds less of nitrogen for 
the plot receiving air-slaked lime. Experiments at the Maryland 
Station gave larger yields for ground limestone. 



REFERENCES 

^ Hilgard, E. W., Soils, 1906, p. 364. 

''Miller, M. F., Circular 69, Missouri Station, The Fertility of the Soil, 

1914, p. 6. 
»Averitt, A. D., Bulletin 193, Soils of Kentucky, Kentucky Station, 1915, 
p. 141. 

General References. — Hopkins, Cyril G., Soil Fertility and Perma- 
nent Agriculture, 1910. Van Slvke, Lucius L., Fertilizers and Crops, 1915. 
Hall, A. D., The Soil, 1912. Whitson, A. R., and Walster, H. L., Soils 
and Soil Fertility, 1912. 



APPENDIX II 



407 



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408 



APPENDIX II 



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APPENDIX II 409 

Average Yield of Wheat Per Acre for Ten Years (1905 to 1914) * Bushels 



United 

States 


Russia 
(European) 


Germany 


Austria 


Hungary 
proper 


France 


United 
Kingdom 


14.8 


9.9 


30.7 


20.0 


18.1 


20.1 


33.4 



* Yearbook U. S. D. A., 1915. 



APPENDIX III 

The following maps are taken from the Yearbook of the United 
States Department of Agriculture for 1915 : 




410 



APPENDIX III 



411 




412 



APPENDIX III 




APPENDIX III 



413 



' ■'_ t 




a 




414 



APPENDIX III 




:^1 



^ 




' r t 



APPENDIX III 



415 




.416 



APPENDIX III 




APPENDIX III 



417 




INDEX 



Ablation swamp, 30 
Absolute specific gravity, 175 
Absorbents, factor \n conserving 

manure, 165 
Absorption and radiation of heat, 
effect of, on soil temperature, 302 
Acclimated seed, desirable on dry 

land, 255 
Accumulations in pastures, aid in 
maintaining organic-matter con- 
tent, 160 
Acid, chromic, method of determina- 
tion of organic matter, 154 
phosphate, 402 
Acids, decomposition of rocks by, 19 
carbonic, hydrochloric, nitric, 
sulfuric, 20 
Acre-inches, 192 

Adaptation of region to dry farm- 
ing, factors in, 238 
evaporation, 24 1 
rainfall, 238 
soils, 241 
Adobe. 65 

Adsorption by colloids, 132 
Aeration and soil air, chapter on, 
309 
affecting bacteria, 320 
aided by drainage, 223 
or soil ventilation, 311 

accomplished by atmospheric 
pressure, changes in, 311 
diffusion, 311 
removal of water, 311 
temperature changes, 312 
tillage, 313 
■ wind movement, 313 
Aftonian Inter-glacial Stage, 46 
Agassiz, Lake, 38 

extent of, 46 
Agencies of weathering, chemical, 19 

physical, 12 
Agricultural provinces, 383 
Agriculture, drv-land, chapter on, 
238 
permanent, 389 
Air in soils, amount of, 309 

convection currents of, source of 
loss of heat, 296 



Air in soils, composition of. 310 

use of, 309 
Alfalfa, completely killed by heaving, 
226 
crop for dry land. 253 
Alkali, area, absence of vegetation 
on, 286 
black, neutralization of, 281 
effect of irrigation on rise of, 
281 
on foliage of apricot trees, 

283 
on plants. 282 
kinds of. 280 

land, growth of barley on, partly 
and fully reclaimed, 288 
reclaimed, wheat on. 289 
lands, and their reclamation, 
chapter on, 278 
utilization and reclamation 
of, by removal of alkali 
salts, 285 
growing alkali - resistant 

crops, 285 
neutralizing black alkali, 

286 
plowing deep and turning 

alkali under, 286 
retarding evaporation, 285 
limit for germination and 

growth, 284 
origin of, 278 

resistant crops, growing of, 285 
rise of, prevented by cultivation, 
286 
drainage, 226 
salts, removal of. by cropping, 
draining, flooding, leaching, 
scraping, 287 
soils of humid regions, reclama- 
tion of, 290 
spot, beginning of, 279 
turning under of, 286 
Alluvial soils, 38 
Alluviation by glacial stream. 62 
Altitude, affecting organic content of 

soils, 145 
Ammonia, effect on flocculation, 137 
Ammonification, 318 

419 



420 



INDEX 



Ammonium sulfate, 399 
Ampliibole, 3 

Analyses, chemical, of adobe, 65 
Analysis, mechanical or physical, 
123 
phj'sical, systems of, 124 
Andesite, 7 

Animals, decomposition by, 23 
Apatite, calcium phosphate, "i 
Appalachian Mountain and Plateau 

Province, 81 
Apparent specific gravity, 175 
Aqueous rocks, 7 

Area, aird projects, irrigation. 258 
internal, of soil types calculated 
from i^hysical composition, 
182 
of soil surveyed in the United 
States by Bureau of Soils to 
1915, 78 
of spheres, columnar arrange- 
ment, 181 
or internal surface, 181 
Ai-id soils, 74 

nitrogen in humus of, 147 
subsoils, and humid, 70 
Arrangement of particles, 179 

columnar, area of spheres, 181 

or vertical, 180 
oblique, 180 
Artificial mulch, defined, 233 
Aspirator, King's, 128 
Atkinson, A., and Nelson, J. B., stor- 
ing rainfall, Montana, 248 
Atlantic and Gulf Coastal Plains 

Province, 91 
Atmosphere, carbon dioxide in, 20 
Atmospheric pressure, changes in, 
factor in aeration, 311 
effect on percolation, 219 
Auger, soil, 119 
Available moisture, 214 

increased by drainage, 223 
Averitt, A. D., plant food in soil 
areas of Kentucky, 393 

Babb, table, sediment carried by 

streams, 35 
Bacteria, conditions for development, 
319-321 
aeration, 320 
food, 319 
light, 321 
moisture, 319 



Bacteria, conditions for develop- 
ment, physical composition 
of soil, 321 
reaction, 320 
temperature, 320 
distribution of, 318 
number of, effect of lime upon, 
321 
per gram of air-dry soil, 319 
Bacterial action, eftect of potassium 

carbonate upon, 321 
Barley, yield of, continuous cropped 

vs. after fallow, 249 
Barnyard manures, 161 
Barometric pressure, changes in, 

factor in aeration, 311 
Bartlett, W. H., expansion of rocks 

on heating, 13 
Basalt, 7 
Basic slag, 402 
Bates, with Lynde, osmosis in soils, 

212 
Beach or Marram grass, transplant- 
ing, 56 
Beavers, J. C, manure excreted by 
farm animals, 1G2 
value of increase for manure, 
heavy and light applications, 
168 
Bennett, H. H., Bureau of Soils, soil 

survey, 78-111 
Biological eflfects of organic matter, 

ioO 
Biotite, black mica, 4 
Black alkali, neutralization of, 286 
Black locusts, hold sand, 59 
prevent washing, 368 
'• Blowout," in sand dune, 59 
Bog, climbing, 28 

quaking, 28 
Bogs, see hummocks, 30 
Boiling and freezing points, colloids, 

effect on, 131 
Bone meal, 400 
Boulder, granite, 51 

limestone, showing glacial 
scratches, 42 
Boulders, from moraine, 51 
Bouyoucos, G. J., effect of color on 
radiation, 295 
on temperature of sands, 
302 
specific heat of soil constituents, 
299 



INDEX 



421 



Bouyoucos, G. J., time for heat to 

penetrate soil, 306 
Briggs, L. J., ratio between viscosity 
and flow of water, 219 
thickness of liygroscopic film, 
194 
Briggs, Martin, and Pearce, Bureau 
of Soils, sizes of particles, 
124 
chromic acid method of deter- 
mining organic matter, 154 
Briggs and McLane, moisture equiv- 
alent centrifuge, 202 
Briggs and Shantz, water require- 
ment of plants, Alvron, 
Colorado, 242 
wilting coefficient, 212 

determination of, 197 
Brown, E. E., with Schreiner, 0., 

progress of humification, 146 
Brown, P. E., bacteria per gram of 

air-dry soil, 319 
Brownian movement, 130 
Buckingham, little loss of water by 

interstitial evaporation, 232 
Bureau of Soils 

centrifugal m.ethod of physical 

analysis, 127 
classification of soils, chapter 

on, 78 
grades of soil particles, 124 
provinces, soil 

Appalachian Mountain and 

Plateau, 81 
Atlantic and Gulf Coastal 

Plains, 91 
Glacial and Loessial, 84 
Glacial Lake and River Ter- 
race, 89 
Limestone Valleys and Up- 
lands, 83 
Piedmont Plateau, 79 
River Flood Plains, 97 
regions, soil 

Arid Southv/est, 106 
Great Basin, 106 
Great Plains. 100 
Northwest Intermountain, 

105 
Pacific Coast, 107 
Rocky Mountains, 104 
series, soil 

Acadia, 92 
Alamance, 79 
Altamont, 107 



Bureau of Soils, 
series, soil 

Amarillo, 103 
Arkansas, 104 
Bangor, 84 
Bates, 100 
Benton, 101 
Berks, 81 
Bibb, 97 
Billings, 105 
Bingham, 106 
Blanco, 97 
Boise, 105 
Boone, 101 
Brennan, 92 
Brooks, 83 
Caddo, 92 
Cahaba, 97 
Caldwell, 106 
Cameron, 97 
Canyon, 102 
Caribou, 84 
Carrington. 84 
Cazenovia, 85 
Cecil, 79 
Chehalis, 110 
Chenango, 89 
Chester, 80 
Cheyenne, 104 
> Clark, 101 
Clarksville, 83 
Clyde, 89 
Colbert, 83 
Colby, 102 . 
Coloma, 85 
Colorado, 103 
Conasauga, 81 
Conestoga, 83 
Congaree, 97 
Corning, 107 
Cossaymna, 85 
Coxville, 92 
Crawford, 101 
Crowley, 93 
Dawes,' 103 
Decatur, 83 
DeKalb, 81 
Dunkirk, 90 
Durham, 80 
Dutchess, 85 
Duval, 93 
Durant, 93 
Edna, 93 
Elkton, 93 



422 



INDEX 



Bureau of Soils, 
series, soil 

Englewood, 101 
Ephrata, 105 
Eppi:.g, 101 
Everett, 108 
Fargo, 90 
Fayetteville, 82 
Flushing, 85 
Fox, 90 
Iresno, 108 
Frio, 98 
Ganett, 103 
Genesee, 98 
Gila, 107 
Glendale, 107 
Gloucester, 85 
Goliad, 93 
Greensburg, 103 
Greenville, 93 
Hagerstown, 83 
Halston, 98 
Hanceville, 82 
Hanford, 108 
Hesson, 108 
Holyoke, 86 
Houston, 93 
Huntington, 98 
Imperial, 107 
Indio, 107 
Iredell, 80 
Jordan, 106 
Kalmia, 98 
Kewaunee, 86 
Knox, 86 
Lackawanna, 86 
Lake Charles, 94 
Lansdale, 80 
Laramie, 105 
Laredo, 98 
Laurel, 104 
Leonardtown, 94 
Lexington, 86 
Lincoln, 104 
Lintonia, 98 
Louisa, 80 
Lufkin, 94 
Lynden, 109 
Manchester, 90 
Manor, 80 
Maracopa, 109 
Marion, 86 
Marshall, 86 
Maverick, 94 
Meigs, 82 
Melbourne, 108 



Bureau of Soils, 
series, aoil 

Memphis, 87 
Merrimac, 90 
Mesa, 105 
Miami, 87 
Miller, 98 
Mohawk, 87 
Monroe, 94 
Morton, 101 
Myatt, 99 
Nueces, 94 
Ocklocknee, 99 
Oktibbeha, 95 
Olympic, 109 
O'Neill, 102 
Ontario, 87 
Orangebvirg, 95 
Orono, 90 
Osage, 99 
Oswego, 101 
Oxnard, 109 
Penn, 80 
Pierre, 101 
Placentia, 109 
Plainfield, 90 
Plvmouth, 87 
Po'dunk, 99 
Porters, 82 
Portsmouth, 95 
Pratt, 103 
Puget, 1 1 1 
Putnam, 87 
Quincy, 105 
Redding, 110 
Richfield, 103 
Richland, 87 
Rosebud, 103 
Ruston, 95 
Sacramento, 111 
Salem, 111 
San Antonio. 95 
San Joaquin, 109 
San Luis, 104 
Sarpy, 99 
Sassafras, 95 
Scranton, 96 
Sharkev,' 99 
Shelby' 88 
Sidney, 101 
Sioux, 91 
Stockton, 110 
Summit, 102 
Superior, 91 
Susquehanna, 96 
Talladega, 82 



INDEX 



423 



Bureau of Soils, 
series, soil 

Tifton, 96 
Trinity, 99 
Tripp, 104 
Trumbull, 88 
Union, 88 
Upshur, 8-: 
Uvalde, 99 
Valentine, 102 
Vergennes, 91 
Vernon, 102 
Victoria, 96 
Volusia, 88 
Wabash, 99 
Wade, 104 
Walla Walla, 105 
Waukesha, 91 
Waverly, 100 
Webb, 96 

Westmoreland, 82 
Whatcom, 110 
Wheeling, 100 
Williams, 88 
Willows, 110 
Wilson, 96 
Winchester, 105 
Wooster, 88 
Yakima, 100 
Yazoo, 100 
Yolo, 110 
York, 81 
Yuma, 107 
Zapata, 103 

Calcareous rocks, chalk, marl, 8 
Calcite, calcium carbonate, 5 
Calcium carbonate, calcite, 5 

carried by Thames River, 23 
concretions, 62 
cyanamid, 400 
magnesium carbonate, dolo- 
mite, 5 
sulfate, gypsum, 5 
Call, L. E., methods of preparing 

land for wheat, 347 
Campbell, H. W., pioneer in dry 
farming, 247 
subsurface packer, 247, 337 
Canals, loss of Avater from, 266 
Capillarity, amount of water moved 

by, 210 " 
Capillary lift of soil constituents, 
212 
pull of soils, 211 



Capillary capacity or moisture-hold- 
ing capacity of soils, 209 
rise of water in glass tubes, 
height of, 199 
rapidity and height in dif- 
ferent soils, 207 
water as films or waists about 
particles, 200 
in covered and uncovered 

soil, 204 
of soils, chapter on, 199 
movement, affected by or- 
ganic matter, 206-208 
substances in solution, 205 
temperature, 204 
texture, 206 
thickness of film, 203 
viscosity, 204 
use of, 212 
Carbonated water, almost universal 

solvent, 20 
Carbon dioxide 

aid in solution, 22 
brought to earth in precipi- 
tation, 20 
decomposition by, 20 
in rain and snow water, 20 
soil air and atmosphere, 20 
Catch and cover crops, 161 

aid in preventing erosion, 

362 

Gates, J. S., and Cox, H. R., results 

of corn cultivation, 28 states, 353 

Caves, due to action of carbonated 

water, 22 
Centers of accumulation!, Oordil- 
leran, Keewatin, Labra- 
dorean, 45 
map of, 47 
Centrifugal elutriator, Yoder's, 128 
method of physical analysis, 
Bureau of Soils, 127 
Chains, for puddling mud of canals 

to prevent seepage, 267 
Chalk, 8 
Characteristics of water, physical, 

186 
Chemical agencies of weathering, 19 
changes in soil, source of heat, 

294 
precipitates, 8 
Chernozem soils, roots and humus 

in, 144 
Chester, F. E., effect of lime upon 

number of bacteria, 321 
Chicago, Lake, 38 



424 



INDEX 



Chromic acid, and combustion 
methods, comparison, or- 
ganic matter, 155 
method of determination of 
organic matter, 154 
Churn elutriator, physical analysis, 

Hilgard, 120 
Cippoletti or trapezoidal weir, 269 
Classes, types and phases, irt Illi- 
nois, 114 
Clay, defined, 134 
dunes, 53 

effect of, on shrinkage, 133-135 
loams, 115 
tight. OS 
Clays, 114 

and clay loams, properties of 
coagulation or floccu- 
lation, 137 
plasticity, 135 
puddling, 136 
shrinkage, 135 
tenacity, 134 
Clark, F. W., composition of known 

earth, 2 
Classification of soils, by Bureau of 
Soils, chapter on, 78 
based on color, 77 
geology, 72 
lithology, the parent 

rock, 73 
moisture, 73 
temperature, 73 
texture, 77 
vegetation, 75 
need of, 72 
Cleavage, vertical, characteristic of 

deep loess, 03, 64 
Coagulation or flocculation of clavs, 

137 
Coal, formation of, from organic mat- 
ter, 146 
Coffey, G. N., dark color indicating 
outcrop of limestone, 177 
lime and magnesia in soils, 75 
mineral content of soils, 74 
reports clay dunes in Texas, 53 
soluble salts in soils, 74 
Colloids, affecting- hygroscopic moist- 
ure, 195 
dialysis and diffusion of, 131 
examples of, 129 
in soils, 132 

organic and mineral, 132 
properties of, 130 
adsorption, 132 



Colloids, properties of, boiling point, 
efi'ect on, 131 
Brownian movement, 130 
dialysis, 130 
difi'usion, 130 
electrical behavior, 131 
freezing point, effect on, 131 
shrinkage, 132 
size of particles, 130 
Colluvial soils, 30 
Color of soils, 176 

changed by erosion, 361 
effect of deoxidation on, 21 
on temperature, 303 
of sands, 302 
factor in classification, 77 
Colorado mud-flow, 34 
river, work of, 17 
Grand Canon, 17 
Columbia glacier, over-riding forest, 
Alaska, 14 
front of, 15 
Columnar arrangement of particles, 

180 
Combustion and chromic acid 
methods, comparison, organic 
matter, 155 
in oxygen determination of or- 
ganic matter, 154 
Compacters, bar roller, 337 
corrugated roller, 336 
cultipacker, 336 
drum roller, 335 
plankers, 337 
subsurface packer, 337 
Compacting the soil, a part of till- 
age, 326 
increases moisture capacity, 
230 
Composition of feldspars, 3 
fresh manure, 163 
known earth, 2 
river sediments, 262 
Concrete dams for filling gullies, 373 
Concretions, calcium carbonate, 63 

iron, 64 
Conductivity of soil, effect of, on 
temperature, 306 
material, 306 
Constituents of soils, mineral, chap- 
ter on, 123 
organic, chapter on, 142 
Contour plowing, deep, aid in check- 
ing erosion, 364 
seeding, aid in checking erosion, 
365 



INDEX 



425 



Control of moisture, chapter on, 222 
Cordilleran center of accumulation, 

45 
Corn, acreage, 1909, 412 
belt rotations, 382 
comparison, cultivated, scraped, 

weeds allowed to grow, 351 
cultivation, 353 

effect on yield of root pruning 
and deep and shallow cultiva- 
tion, '355 
grown on dry land, 252 

on swamp land, effect of po- 
tassium on, 404 
method of preparing seed bed 

for, 348 
planter, 338 
production, 1909, 413 
results of cultivation, 352 
yields of, different methods of 
tillage, 354 
Cotton belt, rotation for, 384 
Cottrell, H. M., pounds seed per acre 

for different crops, 255 
Cover and catch crops, 161 
Cox, H. R., with Cates, J. S., re- 
sults corn cultivation, 28 states, 
353 
Cracks, in black clay loam, 136 

shrinkage, effect of, on percola- 
tion, 219 
Cropping, alternate vs. continuous, 
yields, 250 
continuous vs. after fallow, 

wheat yields, Montana, 248 
loss of organic matter, due to, 

151 
systems of, 248 
Crop requirements, plant food, 390 
Crops, alkali-resistant, growing of, 
on alkali land, 285 
catch and cover, 161 
deep rooting, effect of, 345 

on moisture capacity, 171 
for dry farming, see dry-farm- 
ing crops 
for irrigated land, see irrigated 

land, crops for 
non-tilled, factor in maintain- 
ing organic matter, 171 
plant food in, 390 



Crops, protection from erosion by 
catch and cover, 362 
meadows and pastures, 361 
rotation of, aid in maintaining 

organic matter, 171 
ten-year average yield of, by 
states in United States, 407, 
408 
Crystalloids, dialysis and diffusion 

of, 131 
Cultivation after irrigation, 273 
and summer tillage in dry farm- 
ing, 246 
level, 355 
object of, 350 
of corn on gray silt loam on 

tight clay, yields, 353 
of corn, Illinois yields, 352 
results of deep and shallow, with 
and without root pruning, 
corn, 355 
ridged, 356 
Cultivators, 337 
blade, 339 
disk, 339 
shovel, 338 
weeder, 340 
Cmnulose soils, 27 
Currents of air, convection, source 

of loss of soil heat, 296 
Cyanamid, calcium, 400 

Dams, for filling gullies, concrete, 
273 
earth, 271, 272 
Deacon, G. F., relation between ve- 
locity and amount of ma- 
terial carried bv streams, 33 
Debris cliff, 30 

Decomposition, effect of, on loss of 
constituents of rock, 22 
of organic matter by drainage, 

225 
of rocks, 11 
by acids, 19 
by animals, 25 
by plants, 25 
through solution, 22 
Deep-rooting crops, effect of, 345 

on water capacity of soil, 
231 
Deherain, effect of aeration on nitri- 
fying bacteria, 320 
loss of nitrates by leaching, 322 
Denitrification, nitrates lost by, 323 



426 



INDEX 



Densitj', with surface tension of 

solutions, 20G 
Deoxidation, 21 
Deposits, eolial, 53 

glacial or ice- laid, chapter on, 
41 
Determination of humus, 156 
Diabase, 7 

Dialysis and diffusion, colloids, crys- 
talloids, 131 
of colloids, 130 
Diffusion, factor in aeration, 311 

temperature for, 298 
Digestibility of feeds, 162 
Diorite, 7 

Disintegration by plants, 19 
by waves, 18 
by wind, 18 
of rocks, 11, 32 
Distribution of alkali, vertical and 
horizontal, 281 
of irrigation water, 268 
Ditches, open drains, 226 
Dobeneck, hygroscopic moisture in 
relation to relative humidity, 
196 
Dolomite, calcium magnesium car- 
bonate, 5 
Dorsey, C. W., reclamation of alkali 
land by underdrainage, 289 
alkali at Maryland station, 290 
Drain gages, 220 
Drainage, chapter on, 222 

benefits of, aeration improved, 
223 
alkali, rise of, prevented, 226 
decomposition and nitrifica- 
tion increased, 225 
erosion decreased, 226 
granulation improved, 222 
heaving reduced, 225 
moisture, available, in- 
creased, 222 
stability increased, 222 
temperature raised, 225 
effect of, on germination and 
growth, 223 
on soil temperature, 301 
from 8 feet of saturated sand, 

221 
types of, open or ditches, 226 
tile, 228 
Drains, see Drainage 
Drills, seeders, 337 
Drumlins, 44 

formation of, 45 



Diy-farming, crops for alfalfa, 253 
barley, 251 
corn, 251 
enimer, 252 
kafir, 252 
milo maize, 252 
oats, 251 
potatoes, 253 
rye, 251 
sorghum, 252 
spelt, 252 
wheat, 250 
deep, medium-grained soil well 
adapted to, 243 
Dry-land agriculture, chapter on, 

238 
Dumont, effect alkaline carbonate on 

nitrate production, 321 
Dunes, clay, sand, silt, 53 
permanent or fixed, 55 
wandering, migatory, 54 
Dupre, with Lynde, capillary pull, 
211 
osmosis in soils, 212 
Dust and loess, physical analysis of, 
64 
storm, 54 
volcanic, 65 
Dynamiting of soils, 345 

Earth, composition of, 2 

dam for filling gullies, 371, 372 
Earth's crust, elements of, 1 
Earthworms, aid in soil formation, 
315 
effect of, on soil, 25 
Eel-grass, 37 
Elements of earth's crust, 1 

plant food, 390 
Electrical behavior of colloids, 133 
Elutriator, method of physical analy- 
sis, Schune, 124 
churn, Hilgard's 126 
centrifugal, Yoder's, 128 
Eolial deposits, or wind-laid soils, 
53 
adobe, in part, 64, 65 
loess, 60-64 
sand, 53-64 
volcanic dust, 65 
Eroded hill lands, yield from, 360 
soil once forested, China, 359 
Erosion, chapter on, 357 
cause of, 

rainfall, character of, 359 
texture and structure of soil, 
358 



INDEX 



427 



Erosion, cause of, topography, effect 
of, 358 
vegetative covering, 359 
checked by brush, 372 
decreased by drainage, 226 
by organic matter, 150 
headwater, 372 
in pasture, 370 
kinds of, sheet, 361 

gullying, 309 
of streams, 16 
old-lield in Mississippi, 370 
organic matter lost by, 151 
results of, color of soil changed, 
361 
organic matter and nitrogen 

removed, 360 
physical character of soil 
changed, 360 
sheet, methods of prevention and 
reclamation, contour 
seeding, 305 
crops, protection by, 

361 
deep contour plowing, 

364 
limestone, application 

of, 361 
organic matter, in- 
creasing, 363 
reforesting, 369 
residues, 363 
terracing, 365 

tiling, 369 
Eruptive rocks, 6 
Esker, Adeline, 44 

material composing it, 45 
formation of, 45 
Evaporation, effect of, on soil tem- 
perature, 300 
factor in adaptability of a re- 
gion to dry farming, 241 
from a free-water surface and 

rainfall, 241 
large loss from, in dry farm- 
ing, 243 
loss by, effect on transpira- 
tion, 191 
of water, cools soil, 296 
prevented by mulches, 232 
rainfall and, Rothamsted, 211 
rainfall and percolation, Roth- 
amsted, 220 
retarding of, factor in cropping 
alkali land, 285 
Everglades, Florida, 29 
Exfoliated granite in California, 13 



Expansion, enormous, due to hydra- 
tion, 21 
due to oxidation, 21 
of rocks, 13 
Expressing moisture content, waya 
of, 191 

Fall plowing, 342 

Fallow, continuous vs. after, wheat 

yields, Montana, 248 
Fallowing, loss of organic matter 

by, 153 
Farm land, value per acre, 410 

property, value per acre, 411 
Feeds, digestibility of, 102 
Feldspars, 3 

composition of, 3 
Fermentation in manure, factor in 

loss of organic matter, 164 
Fertility in Illinois soils, 394-396 
Films and waists of water about 
particles, 200 
thickness of, in soil column, 201 
Fine sandy loams, 116 
Fippin, E. O., with Lyon, T. L., sur- 
face tension and density of cer-- 
tain solutions, 200 
Fires, organic matter lost by, 152 
Fischer, carbon dioxide in rain and 

snow water, 20 
Flocculation, effect of ammonia, 
lime, gypsum, sodium carbon- 
ate on, 137 
or coagulation of clays, 137 
Flooding orchards, basin system, 270 
Florida everglades, 29 
Flow of water, comparison between 

computed and observed, 129 
Food for bacteria, 319 
Forbes, R. H., value of material car- 
ried by Salt River, 262 
Forest, being buried by sand dune, 55 

resurrected, 55 
Fragmental deposits, 8 
Freezing and boiling points, col- 
loids, effect on, 131 
and thawing, 14 

effect on water-logged soil, 223 
Furrow irrigation of potatoes, 271 

Geological classification of soils, 72 
Georgeson, influence of manure on 

soil temperature, 294 
Germination and growth, effect of 
drainage on, 223 
limit of alkali for, 284 
temperature for, 296 



428 



INDEX 



Gilbert with Lawes, transpiration, 

188 
Glacial and loessial province, 84 
drift, gravelly phase, 41 
grooves, striae, 43 
lake and river terrace province, 

89 
lakes, 50, 51 

extent of, 46 
or ice-laid deposits, chapter on, 

41 
period, 45 

scratches on boulder, 42 
stream, alluviation by, 62 
Glaciation, extent of, in North 
America, map of, 46 
in Europe, map of, 48 
Glaciations, lUinoisan, 47 
lowan, 48 

Jerseyan or Nebraskan, 46 
Kansan, 46 
Wisconsin, Early, 50 
Late, 50 
Glacier, Chenega, 41 
Columbia, front, 15 

over-riding forest, Alaska, 14 
defined, 16 

factor in weathering, 15 
incidental features, 50 
pressure of ice, 16 
Grand Cafion, Colorado River, 17 
Granite, 7 

exfoliated, California, 13 
wind-carved, 18 
Granulation, effect of drainage on, 
222 
of organic matter on, 148 
of, on percolation, 218 
Grass, beach or Marram, transplant- 
ing, 56 
bunch, holds sand, 60 
Gravel and gravelly loams, 139 
Gravelly loams, 116 
Gravels, 116 

Gravitational water, chapter on, 217 
Gravity-laid soils, 30 
Great Basin region, 106 

Plains region, 100 
Green manures, 160 
Growth and germination, eflfect of 
drainage on, 223 
color of soils on, 303 
of plants, limit of alkali for, 

284 
temperature for, 297 
Guide-row terrace, 365 
Gulf Coastal Plains, and Atlantic, 91 



Gullying, methods of prevention and 
filling, dams, 371 

soil, 374 

straw and brush, 370 

vegetation, 374 
Gypsum, 5 

Haberlandt, time required for ger- 
mination at different tempera- 
tures, 297 
Hall, A. D., rainfall and evapora- 
tion, Rothamsted, 211 
table, rainfall, percolation, evap- 
oration, Rothamsted, 220 
temperature of soil for growth, 

298 
yield of wheat with percolation 
large and small, 153 
Hardness of minerals, 2 
Hardpan, 69 

effect of, in alkali lands, 290 
Harrows, acme or blade, 333 
disk, 334 
spike- tooth, 331 
spring-tooth, 332 
Hay and pasture province, rotation 

for, 386 
Heat, absorption and radiation of, 
effect on soil temperature, 302 
and cold, factor in disintegra- 
tion, 12 
conduction downward into soil, 

source of loss, 296 
soil, sources of, 293 
specific, affecting soil tempera- 
ture, 298 
effect of moisture on, 300 
of common substances, 299 
of soil constituents, 299 
of soils, 300 
to penetrate soil, time for, 306 
Heaving, due to lack of drainage, 
225 
of alfalfa, 226 
" Heavy " soil, defined, 134 
Hellriegel, water transpired per 

pound of dry matter, 188 
Hematite, 5 

Hilgard, E. W., changes in organic 
matter, 146 
churn elutriator, 126 
composition of salts in alkali 
spot, 282 
of typical alkali salts, 280 
effect of various substances on 
hygroscopic capacity, 195 . 



INDEX 



429 



Hilgard, E. W., fertility in Russian 
soils, 392 
force exerted by roots in pene- 
trating soilj 19 
grades of soil particles, system 

of, 124 
highest amount of alkali with 

plants unaffected, 284 
hygroscopic capacity of soils, 

194 
nitrogen content of humus, 194 
on use of hygroscopic moisture, 

198 
roots and humus in Russian 

soils, 144 
vertical distribution of alkali, 
281 
Hopkins, C. G., grades of particles, 
system of, 124 
production of sweet clover per 
acre, 173 
Humid and arid subsoils, 70 
regions, alkali of, 290 
soils, 75 

nitrogen in humus of, 147' 
Humidity, affecting hygroscopic 

moisture, 196 
Humification, progress of, 146 
Hummocks, called bogs, 30 
Humus, defined, 142 

determination of, 156 
in Chernozem soils, 144 
nitrogen content of, 147 
Hydration, 21 
Hydrochloric acid, decomposition 

by, 20 
Hygroscopic capacity of soils, 194 
coefficient from other constants, 
formulae, 197 
of soils, 196 

relation to wilting coefficient, 
197 
moisture, affected by colloids, 
195 
by humidity, 196 
by organic matter, 196 
by size of particles, 194 
by temperature, 195 
chapter on, 194 
use of, 197 

Ice-laid deposits, chapter on, 41 
Igneous rocks, 6 
Ignition, loss on, 154 
Implements of tillage, compacters, 
335 



Implements of tillage, cultivators, 
337 
harrows, 332 
listers, 332 
plows, 327 
seeders, 337 
Insects, controlled by rotation, 377 

mix soil, 315 
Interglacial stages, Aftonian, 46 
Peorian, 48 
Sangamon, 47 
Yarmouth, 46 
Internal area or surface, 181 
Intrusive rocks, 6 
lowan glaciation, 48 

important loess deposit con- 
nected with, 62 
Irrigated land, crops for, alfalfa, 275 
cereals, 273 
forage crops, 275 
fruits, 275 
sugar beets, 275 
vegetables, 275 
Irrigation, chapter on, 257 

by overhead spray or sprink- 
ling, 272 
canals lined with concrete, 258 
cultivation after, 273 
effect of, on rise of alkali, 281 
in humid climates, 275 
methods of, flooding, 270 
furrow, 271 
sprinkling or overhead sprays, 

272 
sub-irrigation, 272 
potatoes by furrows, 271 
preparation of land for, 259 
projects in United States, 257 
in varied quantities, yield of 

dry matter, 264 
sources of, diversion of 
streams, 258 
pumping from streams or 

canals, 259 
reservoirs, 259 
subterranean supply, 259 
water, character of, 261 
time of, 263 
Illinois soil survey, 112 
Illinoisan glaciation, 47 

Jardine, W. M., yield of milo maize, 

Texas, 253 
Jerseyan or Nebraskan glaciation, 

46 
Johnson, S. W., carbon dioxide in 

soil air, 20 



430 



INDEX 



Karnes, formation of, 45 
Kansan glaciation, 46 
Karraker, substances in solution 
play little part in capillary move- 
ment, 205 
Keewatin center of accumulation, 45 
King, F. H., amount of soil carried, 
Mississippi Kiver, 35 

aspirator, 128 

computed siirfaces of soil par- 
ticles of different kinds of 
soil, 181 

depth of mulches, 235 

difference in temperature due to 
slope, 305 

effect of drainage on tempera- 
ture, 224 

effect of windbreak on evapora- 
tion, 301 

manvire in surface causes rise 
of water into upper three feet, 
212 

movement of moisture from wet 
to dry soil slow, 203, 204 

rain caused rise of water from 
subsoil, 205 

sampling tube, 119 

spring discharge greater with 
falling barometer, 219 

water evaporated with water 
table at varied depths below 
surface, 210 

water used per pound of dry 
matter, 188 

weight of particles with film of 
water, 33 

Labradorean center of accumula- 
tion, 45 
Lacustrine soils, 37 
Lake Agassiz, 38 
beds, 37 
Chicago, 38 

level floor with distinct shore 
line, 37 
filling with peat, method of, 29 
Maumee, 38 

terraces and beaches, 37 
Lakes, ox-bow, 28 
Lands, alkali, 278 
value of, 290 
preparation of, for irrigation, 

259 
surface lowered through solu- 
tion of limestone, 24 



Lang, specific heat of soil constit- 
uents, 299 
Lapham, J. E, and M. H., Bureau of 

Soils, soil survey, 78-111 
•Latitude, affecting organic content 
of soils, 145 
or angle of sun's rays affecting 
soil temperature, 304 
Lawes and Gilbert, water trans- 
pired by growing plants per pound 
of dry matter, 188 
Leaching of manure, factor in loss 
of organic matter, 164 
of soil, organic matter lost bv, 
152 
nitrates lost by, 322 
Legumes, composition of tops and 

roots, 398 
Level bench terrace, 366 
Leverett, F., connects loess with 
lowan glaciation, 62 
depth of drift, Illinois, 42 
run-off for Illinois river basin, 
358 
Light, effect of, upon soil bacteria, 

321 
■' Light " soil, defined, 134 
Liquid manure, value of, excreted 

bv farm animals, 162 
Lime, 403 

and magnesia in soils, 75 
carbonate carried by Thames 

River, 23 
effect of, on number of bac- 
teria, 321 
on flocculation, 137 
forms of, air-slaked lime, lime- 
stone, marl, quicklime, 405 
in prairie compared with tim- 
ber soils, 75 
quick-, loss of organic matter 
due to use of, 152 
Limestone, 403 

addition of, aid in producing or- 
ganic matter, 158 
and rock phosphate, effect of, on 

growth of clover, 159 
application of, aid in preventing 

erosion, 361 
best form to apply, 406 
boulder with glacial scratches, 

42 
ealcite, 5 

composed chiefly of shells, 9 
containing crinoid stems, 9 



INDEX 



431 



Limestone, effect of carbonated 
water on, 22 
factor in maintaining organic 

content of soil, 145 
Valleys and Uplands province, 
83 
Lister, work of, 331 
Lithological factor in classification 

of soils, 73 
Loams, 115 
clay, 115 
gravelly, 116 
peaty, 114 
sandy, 116 
fine, 116 
silt, 115 
stony, 116 
Locust, black, holds sand, 59 

growing on gullied land pre- 
vents erosion, 368 
Loess and dust, physical analyses, 
64 
chemical analyses of, 65 
defined, 61 
deposit, connected with lowan 

glaciation, 62 
deposits, 48 
formation of, 62 
"kindchen," lime concretions, 62 
occurrence of, 61 
origin of, 61 
texture uniform, 64 
ertical walls or cleavage, char- 
acteristic of deep, 63 
Loosening soil, an object of tillage, 

325 
Loss by evaporation, effect of, on 
transpiration, 191 
of manure and its prevention, 

163 
on ignition, 154 

compared with organic mat- 
ter, 154 
Losses of organic matter, 151 
Loughridge, rise of water in clav. 

206 
Lyon, T. L., and Fippin, E. 0., sur- 
face tension and density of certain 
solutions, 206 
Lynde and Dupre, capillary pull, 211 

osmosis in soils, 212 
Lysimeters or drain gages, 220 

Macro-organisms, insects, 315 
plants, 316 
rodents, 315 
worms, 315 



Magnesia in prairie compared with 
timber soils, 75 
and lime in soils, 75 
Magnesium carbonate, dolomite, 5 
Magnetite, 6 
Maintaining and increasing organic 

matter in soils, chapter on, 158 
Major crops, defined, 376 
Mangrove marsh, Florida, 37 
Mangum terrace, 366, 367 
Manure, barnyard, 161 

conserved by use of absorbents, 

165 
farmyard, influence of, on soil 
temperature, 294 
nitrogen content of, 399 
fresh, composition of, 163 
green, 160 

loss of, and its prevention, 163 
by fermentation, 164 
by leaching, 164 
organic matter, in rotting of, 
163 
methods of applying, 168 

of handling, 165 
solid and liquid, value of, ex- 
creted by farm animals, 162 
spreader in action, 167 
steer, composition of, after ex- 
posure, 166 
value of increase due to, per 
ton, 168 
Marbut, C. F., and others, area re- 
sidual soils in United States, 
mapped, 27 
Bureau of Soils, soil survey, 78 
Marine soils, 36 
Marl, 8 

Marram, or beach grass, transplant- 
ing, 56 
Marsh, marine, section of, 36 

mangrove, Florida, 37 
Marshes, early stages of formation, 
map, 36 
defined, 27 
Martin, F. 0., and others, chromic 

acid method, 154 
Material in solution in streams, 24 
Maumee, Lake, 38 
Maximum water capacity of soils, 209 
McLane, with Briggs, moistvire 

equivalent centrifuge, 202 
Meadows, hold soil against erosion, 

361 
Measurement of irrigation water, 
268 



432 



INDEX 



Mechanical analysis, methods of, 
124-128 
or physical analysis, 123 
Merrill, G. P., composition of feld- 
spars, 3 
expansion of granite by hydra- 
tion, 21 
glass ground by wind-borne 

sand, 19 
table, chemical analyses of 
loess, 65 
on loss of constituents of 

rocks, 25 
physical analysis of dust, 64 
Merrill, L. A., yield of wheat for 
different depths of plow- 
ing, 245 
methods of seeding, 254 
Metamorphic rocks, 10 
Methods of soil survey, 118 
Mica, black, biotite, 4 

white, muscovite, 4 
Micro-organisms, injurious, 317 

beneficial, 317 
Migratory sand dunes, 58 
Miller, M. F., plant food in Mis- 
souri soils, 392 
Mineral colloids, 132 

constituents of soils, chapter 

on, 123 
content of soils, 74 
phosphorus-bearing, apatite, 5 
soil constituents and their prop- 
erties, 129 
Minerals, dissolved by carbonated 
water, 22 
hardness of, 2' 

iron-bearing, hematite, magne- 
tite, limonite, 5, 6 
soil forming, 1 

specific gravity of, 175 
Minor crops, 376 

Mississippi River, soil material de- 
livered at mouth, 35 
Moisture, available, 214 

increased by drainage, 223 
capacity of soil, methods of in- 
creasing, compacting 
soil, 230 
deep rooting crops, 231 
organic matter, 231 
tillage, 230 
control of, chapter on, 222 

by tillage, chapter on, 230 
content, ways of expressing, 191 



Moisture content, ways of express- 
ing, acre-inches, 192 
cubic inches, or per cent 

of volume, 192 
p.er cent of weighft of 
soil, 191 
decreasing, losses from soils, 

232 
effect of, on specific heat, 300 
equivalent, defined, 202 

determination of, from other 

constants, formulfe for, 203 

equivalents of some soil classes, 

202 
excess of, removed by tillage, 231 
factor in amount of organic 
matter in soils, 143 
soil classification, 73 
for bacteria, 319 
-holding capacity of soils, 209 
hygroscopic, chapter on, 194 
in soil columns, 201 
retained by organic matter, 149 
storing and conserving by till- 
age, 326 
supply in soils, 189 
Moraine, terminal, 43 
^lorrow, G. W., results of root prun- 
ing in shallow and deep cultiva- 
tion of corn, 355 
Moss, sphagnum, 28 
Mucks, 114 

specific heat of, 300 
^h\d flow, Colorado, 34 
3.1uller, Richard, solution of min- 
erals, 22 
Mulch, defined, 233 
depth of, 235 
fineness of, 234 
maintenance of, 236 
soil effectiveness of, 235 
value of, for corn, humid re- 
gions, 350 
IMulches, permit little loss of water 

by interstitial evaporation, 233 
Muscovite, white mica, 4 

Xebraskan glaciation, or Jerseyan, 

46 
Nelson, J. B., with Atkinson, storing 

rainfall, Montana, 248 
Newell, Dr. F. H., directed large 

irrigation projects, 258 
Nitrates lost from soil by leaching, 
322 
by denitrification, 323 



INDEX 



433 



Nitrate production, effect of potas- 
sium carbonate upon, 321 
Nitric acid, amount brought to 
earth, Rothamsted, 20 
decomposition by, 20 
Nitrification, 317' 

increased by drainage, 225 
loss of organic matter by, 152 
temperature for, 298 
Nitrogen, 393 

commercial forms of, ammonium 
sulphate, 399 
calcium cyanamid, 400 
organic substances, 400 
sodium nitrate, 399 
content of humus, 147 
fixation, 317 
furnished to crops by organic 

matter, 151 
in fertilizing materials, 405 
in humus from diff'erent mate- 
rials, 147 
lost by erosion, 360 
Non-tilled crops, factor in main- 
taining organic matter, 171 
Northwestern International Re- 
gion, 105 
Number of particles, 178 

Oats production, 1909, 414 

seed bed for, 349 
Objects of a soil survey, 117 
Oblique arrangement of particles, 

180 
Odor of soils, 177 

Optimum water content, defined, 212 
Organic colloids, 132 

constituents of soils, chapter 

on, 142' 
matter, addition of, as sweet 
clover, 172 
affecting capillary movement, 
206-208 
hygroscopic moisture, 196 
and fertility, loss of, in 

rotting of manure, 163 
and nitrogen, lost by erosion, 

360 
changes of, 145 
comparison, chromic acid and 

combustion methods, 155 
defined, 142 
distribution of, in soil strata, 

147 
effect of, on percolation, 218 

on shrinkage, 130, 135 
in sweet clover, 173 
28 



Organic matter increased by plowing 
under legumes, 172 
increases moisture - holding 

capacity, 231 
increasing amount of, aid in 

checking erosion, 363 
in soils, amount of, depends 
on altitude, 145 
on latitude, 145 
on limestone, 145 
on moisture, 143 
on vegetation, 144 
kinds of, active, coal-like, 

inert, 142 
loss on ignition compared 

with, 154 
losses of, by cropping, 151 
by erosion, 151 
by fallowing, 153 
by fires, 152 
by leaching, 152 
by quicklime, 152 
methods of estimation of, 153 
chromic acid method, 154 
combustion in oxygen, 

154 
loss on ignition, 154 
maintaining, accumulations 
in pastures, 160 
barnyard manures, 161 
catch and cover crops, 

161 
green manures, 160 
limestone, addition of, 

158 
non-tilled crops, growing 

of, 171 
organic residues, use of, 

170 
phosphorus, application 

of, 159 
rotation of crops, 171 
of soils, maintaining and in- 
creasing, chapter on, 158 
turning under and incorpo- 
rating with soil, object of 
tillage, 325 
residues, 170 

substances lower surface ten- 
sion, 205 
source of nitrogen, 400 
Organisms, soil, chapter on, 315 
beneficial. 317 

injurious, as plant diseases, 317 
Origin of alkali, 278 
of soil material, 1 



434 



INDEX 



Osborne, grades of particles, 124 
Osmosis, temperature for, 298 
Osmotic pressure, sugar solution, 

131 
Ox-bow lakes, 28 
Oxidation, 20 

expansion caused by, 21 
loss of organic matter by, -152 
Oxygen, combustion in, determina- 
tion of organic matter, 154 

Packing, subsurface in dry farming, 

247 
Pacific Coast Region, 107 
Particles, colloid, size of, 130 

soil, and their separation, 123 
arrangement of, 179 
number of, 178 
shape of, 178 

size of, affecting hygroscopic 
moisture, 194 
Pastures, accumulations in, aid in 
maintaining organic-matter 
content, 160 
hold soil against erosion, 361 
Patten, H. E., specific heat of soils, 
300 
effect of moisture on specific 
heat, 300 
Pearce, J. R., size of particles, 124 

chromic acid method, 154 
Peat, filling lake, 29 

method of formation, 28 
Peats, 114 
Peaty loams, 114 
Peor'ian interglacial stage, 48 
Percolation, affected by atmospheric 
pressure, 219 
by granulation, 218 
by organic matter, 218 
by physical composition of soil, 

217 
by roots of plants, 219 
by shrinkage cracks, 219 
by viscosity of water, 219 
defined, 217 
evaporation, rainfall, Rotham- 

sted, 220 
large and small, effect of, on 

yield of wheat, 153 
loss of, by water, in dry farming, 

242 
source of loss of water, 232 
Pfeffer, osmotic pressure, sugar 
solution, 131 



Phosphate, rock, and limestone, ef- 
fect on growth of clo- 
ver, 159 
on wheat, 401 
Phosphorus, application of, aid in 
producing organic matter, 159 
forms of, acid phosphate, 402 
basic slag, 402 
bone meal, 400 
compared, 402 
rock phosphate, 400 
in fertilizing materials, 405 
Physical agencies of weathering, 12 
analyses of loess and dust, 64 
analysis, methods of, 124 
aspirator. King's, 128 
centrifugal. Bureau of 
Soils, 127 
elutriator, Yoder's, 128 
churn elutriator, Hilgard's, 
126 
elutriator, Schone, 124 
sieve, 124 
subsidence, 124 
systems of, 124 
changes, source of soil heat, 294 
character of soil changed by ero- 
sion, 360 
of water, 186 
composition of soil in relation 
to bacteria, 321 
affecting percolation, 217 
of soils, varied, effect of, on 
porosity, 184 
condition of soil, effect of al- 
kali on, 280 
or mechanical analysis, 123 
properties of soils, chapter on, 
175 
apparent specific gravity, 

175 
arrangement of particles, 

179 
color, 176 
internal area or surface, 

181 
odor, 177 

number of particles, 178 
porosity, 182 
real specific gravity, 175 
shape of particles, 178 
weight, 176 
Pines growing on sand, 60 
Placing of soil material, chapter 
on, 27 



INDEX 



435 



Plant diseases controlled by rota- 
tion, 377 
food, crop requirements, 390 
elements of, 390 
in crops, 390 

in Illinois soils, surface, 39-4 
subsoil, 396 
subsurface, 395 
in Missouri soils, 392 
in residual soils, 392 
in Russian soils, 392 
locked up in mulches, 236 
supply in soils, 391 
Planting seed accompanied by some 

tillage, 326 
Plants, amount of water required 
by, 187 
disintegration by, 19 
effect of alkali on, 282 

on rocks, 24 
remains benefit soil, 316 
water requirements, 241 
Plasticity of clays, 135 
Plow, an early form of, 340 
pan or sole, 70 
theoretical action of, 327 
Plowing, 340 

deep, and turning under alkali, 
286 
contour, aid in checking ero- 
sion, 364 
tilling, 345 
depth of, 344 
fall, desirable in dry farming, 

246 
good, essentials of, 341 
sod well turned, 341 
poor, crooked furrow, 342 
subsoiling, 345 
time of, 342 
fall, 343 
spring, 344 
yields of wheat for different 
depths of, in dry farming, 245 
Plows, deep tilling double disk, 331 
disk, 329 

general purpose, 328 
lister, 332 
sod, 329 
stubble, 328 
subsoil, 332 
Plutonic rocks, 6 

Pore space, amount of in soils, ISO 
Porosity, different grades of sand, 
183 
of soils, 182 



Porosity of soils, of varied physical 

composition, 184 
Potassium, 403 

effect of, on corn on swamp 

land, 404 
in fertilizing materials, 405 
Potatoes, on dry farm, 253 
Pott, H. E., relative conductivity 

of soil material, 306 
Prairie areas of United States, 76 

soils, 76 
Precipitates, chemical, 8 
Precipitation, map of United States, 
190 
on earth's surface, 189 
source of soil heat, 294 
Preparation of seed bed, 345 
Press drill, 337 

Pressure, atmospheric, changes in, 
factor in aeration, 311 
of waves, 18 
Prestwich, lime carbonate carried 

by Thames River, 23 
Prevention of loss of manure, 163 
Properties, physical, of soils, chap- 
ter on, 175 
Puddling of clays, 136 

prevented by organic matter, 150 
Pulverizing and loosening soil, an 

object of tillage, 325 
Pumping water for irrigation, 259 
Pyroxene, 3 

Quaking bog, 28 
Quartz, 2 

Radiation, factor in loss of soil heat, 
295 

from sun, source of soil heat, 293 

of heat, effect of, on soil tem- 
perature, 302 

ratio, different colored soils, 295 
Rainfall, affecting transpiration, 189 

and evaporation from free-water 
surface, 241 
Rothamsted, 211 

and snow, precipitation on 
earth's surface, 189 

character of, effect on erosion, 
359 

factor in value of region for 
dry farming, 238 

map of United States, 190 

percolation, evaporation, Roth- 
amsted, 220 



436 



INDEX 



Rainfall, storing of, in dry farming, 
247 
types of, over dry-land area of 
United States, 239 
Eeaction, alkaline, of soil desirable 

for bacteria, 320 
Eeade, rate of lowering of land sur- 
face by solution, 24 
Real or absolute specific gravity, 175 
Reclamation of alkali lands, chap- 
ter on, 278 
Redding, R. J., depth of plowing for 

cotton on eroded land, 364 
Reforesting stops erosion, 369 
Reservoirs, storing water for irriga- 
tion, 259 
Residual soils, 27 
Residues, organic, 170 

return of, aid in preventing ero- 
sion, 363 
Resurrected forest, 55 
Rhyolite, 7 
River Flood Plains province, 97 

sediments, composition of, 262 
swamps, 28 

w^ater, suspended matter in, 262 
Rock disintegration and talus slope, 
32 
outcrop, 116 
phosphate, 400 
split by tree, 19 
weathering of jointed, 31 
Rocks, 6 

aqueous, 7 

decomposition and disintegra- 
tion of, 11 
eruptive, 6 

expansion of, on heating, 13 
igneous, 6 
intrusive, 6 

loss of constituents through de- 
composition, 22 
metamorphic, 10 
plutonic, 6 
volcanic, 6 

weathering of, chapter on, 11 
Rocky Mountain and Plateau Re- 
gion, 104 
Rodents, mix surface and subsoil, 

315 
Rogers Brothers, dissolved minerals 

in carbonated water, 2'2 
Rollers, 335 to 337 
Roosevelt dam, 260 
Root injury, 353 

pruning of corn, results, 355 



Root systems, depth of, varied in ro- 
tations, 378 
Roots and tops, legumes, compo- 
sition of, 398 
force exerted by, 19 
in Chernozem soils, 144 
of plants aid percolation, 220 
tree prying rock apart, 19 
Rotation, chapter on, 376 

advantages of, better distribu- 
tion of work, 377 
control of insects and plant 
diseases, 377 
of weeds, 377 
compared with continuous corn, 

Iowa, 379 
effect of, on crop yields, Illinois, 

Ohio, Minnesota, 379, 380 
for corn and winter wheat belt, 
382 
cotton belt, 384 
spring wheat belt, 386 
heljjs maintain good tilth, 378 
organic matter, 378 
produces larger yields, 378 
renders toxic substances less 

harmful, 378 
variation in depth of root 
systems, 378 
of crops, aid in maintaining or- 
ganic matter, 171 
place for crops in, 381 
planning of, 380 
Rotmistrov, weeds enemy of culture, 
friends of drought, 244 
water not raised far by capil- 
larity at Odessa, 210 
Run-off, cause of loss in dry farm- 
ing, 242 
Russell, origin of adobe, 65 

Sage brush on land well adapted to 

dry farming, 239 
Salts, soluble, in soils, 74 
Sampling of soils, 120 
tube. King's, 119 
Sand dune, burying forest, 55 
wind ripples on, 56 
dunes, migratory or wandering, 
54, 58 
permanent or fixed, 54, 55 
held by, black locusts, 59 
bunch grass, 60 
partridge pea, 59 
pines, 60 
sensitive plant, 59 



INDEX 



437 



Sand dunes, held by trailing wild 
bean, 60 
vegetation, 57 
movement checked by fences, 58 
porosity of different grades, 183 
Sands, 116 

and sandy loams, properties 

of, 139 
radiation ratio of different 

colors of, 295 
temperature of, effect of color 
on, 302 
Sandstones, 8 
Sandy loams, 116 
Sangamon interglacial stage, 47 

soil, 49 
Schlosing, relation, nitrates formed 

to oxygen, 320 
Schone's elutriator method, physical 

analysis, 124 
Schreiner, 0., and Brown, E. E., 

progress of humification, 146 
Sedentary formations, 27 
Sediment carried in suspension by 

rivers, 35 
Sedimental soils, 33 
classes of, 36 
Sedimentary, fragmental, 8 
Seed, acclimated, necessary in dry 
farming, 255 
bed, preparation of, for corn, 
348 
for oats, 349 
for wheat, 346 
Seeders, 337 

Seeding, different methods of, yield 

wheat on dry land, 254 

on dry land, 254 

rate per acre, Colorado, 255 

Shaler, wave action, Cape Ann, 

Massachusetts, 18 
Shales, 8 

Shantz, H. L., see Briggs 
Shape of particles, 178 
Shrinkage, affected by colloids, 132 
cracks, 136 

effect of, on percolation, 219 
physical composition of, 
135 
of soils, 135 

different types of soil, 133 
Sieve method, physical analysis, 124 
Silica, 2 

Silt and silt loams, properties of, 
138 
dunes, 53 



Silt loams, 115 
Sink holes, 22 

in cave region, 24 
ponds, produced when outlet 
is clogged, 24 
Size of soil particles, effect of, on 

capillarity, 201 
Slope of land, effect of, on soil tem- 
peratures, 305 
Snyder, loss of organic matter in 
forest fires, 152 
nitrogen in humus from vari- 
ous materials, 147 
Sodium nitrate, 399 
Soil — soils 

air and aeration, chapter on, 
309 
carbon dioxide in, 20 
composition of, 310 
alluvial, 38 
amount of air in, 309 

of organic matter in, 142 
and subsoil, "chapter on, 67 
are they inexhaustible? 289 
arid, 74 
auger, 119 

Bureau of, classification, chap- 
ter on, 78 
carried in suspension by rivers, 

35 
capillary or moisture-holding 
capacity of, 209 
pull of, 211 
character of, factor in its adapt- 
ability to dry farming, 241 
Chernozem, roots and humus in, 

144 
class, defined, 79 
classes in Illinois, 112 
clay loams, 115 
clays, 114 
gravels, 116 
gravelly loams, 116 
loams, 115 
mucks, 114 
peats, 116 
peaty loams, 116 
sands, 116 
sandy loams, 116 

fine, 116 
silt loams, 115 
classification of, chapter on, 72 
colloids in, 132 
colluvial, 30 
color of, 176 

effect on time of germination, 
304 



438 



INDEX 



Soils, compacted by tillage, 326 

conductivity of, effect on tem- 
perature, 305 
constituents, capillary lift of, 
212 
specific heat of, 299 
cumulose, 27 

deep, mediiun-grained, well 
adapted to dry farming; 243 
definition of, 1 

effect of alkali on physical con- 
dition of, 280 
of color of, on growth, 303 
on transpiration, 191 
eolial, 53 

erosion, chapter on, 358 
fertility, appendix I, 389 
-forming minerals, 1 
glacial, 41 
gravelly, not well adapted to 

dry farming, 240 
gravity-laid, 30 
gullies filled with, 374 
heat, loss of, by conduction 
downward into soil, 290 
by convection currents of 

air, 296 
by evaporation of water, 

296 
by radiation, 295 
sources of, 293 

chemical changes, 294 
physical changes, 294 
precipitation, 294 
radiation, direct from sun, 
293 
"heavy," "light," defined, 134 
humid, 75 
hygroscopic capacity of, 194 

coefficient of, 196 
Illinois, fertility in, 394 
Kentucky, 393 
lacustrine, 37 
lime and magnesia in, 75 
marine deposits, 36 
material and its origin, chapter 
on, 1 
placing of, 27 

relative conductivity of, 306 
methods of increasing moisture 

capacity of, 230 
mineral constituents of, chap- 
ter on, 123 
content of, 74 
Missouri, 392 
mulch, defined, 233 
mulches, effectiveness of, 235 



Soils, odor of, 177 

organic constituents of, chap- 
ter on, 142 
organisms, chapter on, 315 
particles and their separation, 
123 
held together by organic mat- 
ter, 151 
surfaces of, in different soils, 
181 
physical character of, changed 
by erosion, 360 
properties of, chapter on, 175 
plant food, supply in, 391 
porosity of, 182-184 
prairie, 75 
provinces, area surveyed to 

1915, 78 
regions, area surveyed to 1915, 

78 
residual, 27 

plant food in, 392 
running together hinders aera- 
tion, 313 
samplers, 119 
sampling of, 120 
Sangamon, 49 
sedimental, 33 

classes of, 36 
series, Bureau of Soils, 79-111 
shrinkage of, 133, 135 
soluble salts in, 74 
specific heat of, 300 
strata, distribution of organic 
matter in, 147 
thickness of, 120 
weight of, 120 
stream-laid, 38 
subsurface, 67 
surface, 67 

survey by rlureau of Soils, chap- 
ter on, 78 
by Illinois Experiment Sta- 
tion, chapter on, 112 
methods of, 118 
objects of, 117 
surveys, 116 

temperature, chapter on, 293 
conditions affecting, 298 
absorption and radiation, 

302 
color, 303 
conductivity, 306 
drainage, 301 
evaporation, 300 



INDEX 



439 



Soils, temperature, conditions af- 
fecting, latitude or angle 
of sun's rays, 304 
slope, 304 
specific heat, 298 
tillage, 307 

water, presence of, 302 
for growth, 298 
for vital functions of plants, 
germination, 296 
growth, 297, 298 
nitrification, 298 
osmosis and diffusion, 
298 
influenced by liquid water, 295 

by manure, 294 
raised by absorption of water 

vapor, 294 
ten-year average, 307 
texture and structure of, effect 

on erosion, 358 
timber, 76 

time for heat to penetrate, 306 
top, 67 

type, defined, 79 
types, classes and phases in Illi- 
nois, 114 
defined, Illinois, 112 
internal area of, 182 
naming of, 113 
ventilation, see aeration, 311 
water of, 186-222 
water-laid, 33 
water-logged, 313 
weight of, 176 
Sole, plow, 70 
Solid manure, value of, excreted by 

farm animals, 162 
Solution, decomposition by, 22 
Specific heat of water, 187 
gravity, apparent, 175 

of soil-forming minerals, 175 
real or absolute, 175 
Sphagnum moss, 27, 28 
Spring plowing, 344 

wheat, acreage, 1909, 415 
region, rotation for, 386 
Stability of soil increased by drain- 
age, 222 
Stalactites, stalagmites, in cavern, 23 
Stones, 139 
Stony loams, 116 
Storm, dust, 54 
Straw, used in filling gullies, 370 



Streams, diversion of, for irriga- 
tion, 258 
erosion of, 16 
-laid soils, 38 
material carried and rolled bv, 

16 
work of, affected by velocity 
of current, 16 
Strise, glacial, on rock surface, 43 
Structure of soil, effect on erosion, 

358 
Sub-provinces, classes, types, sur- 
veys, chapter on, 112 
Subsidence method, physical analy- 
sis, 124 
Subsoil, 68 
plow, 330 

soil and, chapter on, 67 
Subsoiling, 345 
Subsoils, arid and humid compared, 

70 
Substances in solution, effect on vis- 
cosity, 205 
Subsurface packing, 247 

soil, 67 
Sugar beets, returns from thirty 

inches of water, 266 
Sulfuric acid, decomposition by, 20 
Surface, internal, 181 
soil, 67 

tension, affecting capillarity, 
199 
and density of solutions, 206 
Survey, soil, by Bureau of Soils, 
chapter on, 78 
by Illinois Experiment Sta- 
tion, chapter on, 112 
methods of, 118 
objects of, 117 
Surveys, soil, 116 

in different states, 117 
Swamp, ablation, 30 

land, typical Eastern, 29 
wet woods, 30 
Swamps, defined, 27 

river, 28 
Sweet clover on badly eroded land, 
361 
plowed under, 172 
quantity grown per acre, 173 
Syenite, 7 
Systems of physical analysis, 124 

Talus, 30 

slope, 32 
Temperature, chapter on, 293 



440 



INDEX 



Temperature, affecting hygroscopic 
moisture, 195 
viscosity, 204 
changes, factor in aeration, 312 
climate, factor in soil classifica- 
tion, 73 
effect of, on capillary rise of 

water, 204 
for bacterial development, 320 
germination, 296 

table of, 297 
growth, 297 
nitrification, 298 
osmosis and diffusion, 208 
of plowed and unplowed land, 
312 
sands, effect of color on, 302 
soil, conditions affecting, 298 
influenced by manure, 294 
raised by drainage, 224 

by organic matter, 150 
soil, ten-year average, 307 
time required for radicle to ap- 
pear at different, 297 
Tenacity of soils, 134 
Terminal moraine, formation of, 45 

topography of, 134 
Terrace, glacial lake and river prov- 
ince, 89 
near Rockford, Illinois, 38 
Terraced park, Mississippi, 367 
Terraces in China, 364 

kinds of, guide-row, 365 
level beach, 366 
Mangum, 366, 367 
method of formation, 39 
of Frazier River, 38 
Texture of soil, affecting capillary 
movement, 206 
percolation, 217 
effect of, on erosioti, 358 
factor in soil classification, 77 
in relation to bacteria, 321 
Thawing and freezing, 14 
Thickness of film affecting capillary 

movement, 203 
Thorne, C. E., composition of steer 
manure after three months' ex- 
posure, 166 
Thysell, J. C, summer tillage with 
alternate cropping vs. continuous 
cropping, 250 
Tight clay, 68 

Tile drainage, effect of, on topog- 
raphy of water table, 228 
Tile drains, 228 



Tiling, aid in checking erosion, 369 
Tillage, chapter on, 325 

control of moisture by, 230 

deep, in dry farming, 245 

effect of, on soil temperature, 

307 
factor in aeration, 313 
increases moisture capacity, 230 
objects of, compacting soil, 326 
killing weeds, 326 
planting seed, 326 
pulverizing and loosening 

soil, 325 
storing and conserving moist- 
ure, 326 
turning under vegetable mat- 
ter, 325 
removal of excess of moisture 

by, 231 
summer, in dry farming, 246 
with alternate cropping, com- 
pared with continuous 
cropping yields, 250 
Tilling, deep, 345 
Tilth, rotation helps maintain, 378 
Timber areas of United States, 76 

soils, 76 
Time for germination affected by 
color of soil, 304 
at different temperatures, 297 
Top soil, 67 

Topography, effect of, on erosion, 358 
Toxic substances less harmful in 

rotations, 378 
Trachyte, 7 

Transpiration, dependent upon 
evaporation, 191 
soil, 191 

supply of moisture, 189 
from plants, large loss of wa- 
ter, 232 
of water per pound, dry matter 

produced, 188 
source of loss in dry farming, 
244 
Transported formations, 30 
Tull, Jethro, " tillage is manure,'' 

325 
Type, soil, defined, 79 
Illinois, defined, 112 

Udden, J. A., estimate, dust carried 

in air, 53 
Uloth, plants germinated on ice, 296 



INDEX 



441 



Value of increase for manure per 
crop and ton, 168 
organic matter to soils, 148 

binds soil particles to- 
gether, 151 
biological effects, 150 
erosion, loss by, pre- 
vented, 150 
furnishes nitrogen, 151 
granulation affected, 148 
moisture retained, 149 
puddling prevented, 150 
temperature raised, 150 
Van Slyke, L. L., per cent of liquid 
and solid excrement, 162 
composition of fresh manure, 
163 
Vegetation, aid in filling gullies, 374 
factor in soil classification, 75 
source of soil organic matter, 
144 
Vegetative covering, effect on ero- 
sion, 359 
Velocity of current, effect of, on 
size of material carried, 
33 
on work of streams, 16 
Ventilation of soils, 311 
Vertical cleavage or wall, character- 
istic of deep loess, 63 
Viscosity of water, 187 

affecting capillary movement, 

204 
effect of, on percolation, 219 
Volcanic dust, 6 
rocks, 6 

Wandering sand dunes, 54, 58 
Water, amount of, to apply in irri- 
gation, 363 
required by plants, 187 
at different heights above water 

table, drained, 217 
available, 213, 214 
capacity of soils, maximum, 209 
capillary rise of, affected by 
temperature, 204 
in glass tubes, 199 
use of, 212 
comparison between computed 

and observed flow of, 129 
draining from eight feet of satu- 
rated sand, 221 
duty of, 267, 268 



Water evaporated daily per square 
foot of soil, 210 
evaporation of, effect on soil 

temperature, 296, 300 
for irrigation, character of, 261 
gravitational, chapter on, 217 
height and apidity of capillary 

rise in different soils, 207 
in soil in one-foot strata to 8 

feet deep, 248 
irrigation in varied quantities, 

yield of dry matter, 264 
-laid soils, 33 

liquid, effect on soil tempera- 
ture, 295 
-logged soil prevents aeration, 

313 
loss of, by interstitial evapora- 
tion, slight, 233 
from canals, 266 
in dry farming by evapora- 
tion, 243 
by percolation, 242 
by run-off, 242 
by transpiration, 244 
methods of preventing, 244 
deep tillage, 245 
fall plowing, 246 
storing rainfall, 247 
subsurface packing, 247 
summer tillage, 246 
material carried by, 33 
measurement and distribution 

of, in irrigation, 268 
moved by capillarity, amount 

of, 210 
of soils, chapter on, 186 

capillary, chapter on, 199 
physical characteristics, 186 
presence of, effect on soil tem- 
perature, 302 
producing power of, in varied 

application, 265 
removal of excess of, 222 
factor in aeration, 311 
required for corn, Utah, 242 
to produce one pound dry 
matter, 242 
requirement of plants, 241 
river, suspended matter in, 262 
table, topography of, in tiled 

land, 228 
transpired, for one part of dry 

matter produced, 188 
uses of, enumerated, 187 



d42 



INDEX 



Water vapor, increase in tempera- 
ture by absorption of, 294 
viscosity of, 187 
Waves, disintegration by, pressure 

of, 18 
Weathering, advanced, 12 
chemical agencies of, 19 
of rock, irregular due to joints 
and stratification, 11 
jointed, 31 
of rocks, chapter on, 11 
physical agencies, 12 
Weeder, 340 
Weeds, controlled bv rotation, 378 

killing of, object of tillage, 326 
Weight of soil, 176 

strata, 120 
Wheat belt, winter, rotations for, 
382 
effect of rock phosphate on, 401 
methods of preparing land for, 

347 
Minidoka project, Idaho, 261 
production. United States, 1900, 
417 
' • seed bed for, 346 

yield, different methods of seed- 
ing, 254 
of under varied percolation, 

153 
ten-year average, 409 
without irrigation, Montana, 
249 
yields for different depths of 
plowing, 245 
Widtsoe, J, A., dry matter per acre 
from varied amounts of irri- 
gation water, 264 
precipitation on earth's surface, 
189 



Water, producing power of 30 acre- 
inches of water applied to 
varied areas, 265, 266 
rainfall and evaporation from 

free-water surface, 241 
suspended matter in river 

waters, 268 
water in one-foot strata to eight 
feet, 248 
Weir, rectangular, for measuring ir- 
rigation water, 268 
trapezoidal or Cippoletti, 269 
Wild bean, trailing, holds sand, 60 
Wiley, H. W., odor of soils, 177 
Wilting coefficient, defined, 212 

from other constants, for- 
mula?, 213 
of soils for different plants, 

213 
relation of hygroscopic co- 
efficient to, 197 
Wind-carved granite, 18 
disintegration by, 18 
movement, factor in aeration, 

313 
ripples on sand, 56 
Winter wheat acreage, 1909, 416 
Wisconsin glaciations, 50 
Wollny, difference in temperature 
due to slope, 304 
water transpired per pound of 
dry matter, 188 
Woods, swamp, wet, 30 
Work, better distributed by rotation, 
377 

Yarmouth interglacial stage, 46 
Yields increased by rotations, 378 
Yoder, P. A., centrifugal elutriator, 

128 

Zeolites, 4 



